Selective Mutism and Comorbidity With Developmental Disorder/Delay, Anxiety Disorder,

and Elimination Disorder

H A ” E KRISTENSEN, M.D.

ABSTRACT

Objectives: To assess the comorbidity of developmental disorder/delay in children with selective mutism (SM) and to

assess other cornorbid symptoms such as anxiety, enuresis, and encopresis. Mathod: Subjects with SM and their matched controls were evaluated by a comprehensive assessment of the child and by means of a parental structured diagnostic

interview with focus on developmental history. Diagnoses were made according to DSM-IV. Results: A total of 54 children

with SM and 108 control children were evaluated. Of the children with SM, 68.5% met the criteria for a diagnosis reflecting developmental disordeddelay compared with 13.0% in the control group. The criteria for any anxiety diagnosis were met by

74.1% in the SM group and for an elimination disorder by 31.5% versus 7.4% and 9.3%, respectively, in the contrd group. In the SM group, 46.3% of the children met the criteria for both an anxiety diagnosis and a diagnosis reflecting developmen-

tal disorder/delay versus 0.9% in the contrds. Conclusions: SM is associated with developmental disorder/delay nearly as

frequently as with anxiety disorders. The mutisrn may Conceal developmental problems in children with SM. Children with SM often meet diagnostic criteria for both a developmental and an anxiety disorder. J. Am. Acad. ChiMAddesc. Psychiatry;

2O00, 39(2):24%256. Key Words: selective mutism, comorbidrty, developmental disorder/delay.

Children with selective mutism (SM) persistently fail to speak in certain situations (e.g., school) where spealung is expected despite speaking in other situations (e.g., at home) (American Psychiatric Association, 1994). The few previous prevalence studies suggest a prevalence of 3 to 8 in 10,000 (Brown and Lloyd, 1975; Fundudis et al., 1979). However, 2 recent studies indicate that the disorder may be more frequent (Kopp and Gillberg, 1997; Kumpulainen et al., 1998). Although relatively rare, the condition rep- resents a therapeutic challenge, reflected by the consid- erable number of case reports in the literature (Hesselman, 1981; Wright et al., 1994). In contrast, well-controlled studies of larger samples of children with SM are quite sparse, and the pathogenesis is poorly understood. Most authors regard anxiety as the hallmark of SM, and recent

Accrptrd/uly 29, 1999. From Nic. Waali Instituu, Oslo. Thu stuay was supported by the NoruKgian Research Council and the Council

Reprint rrquests to Dr. Krismm. NU. WaaL Institute. p. 6. 143, T h , 0801

0890-8567/00/3902-0249Q2000 by the American Academy of Child

f i r Mental Hralth. Norwq.

Oslo, Norway; r-mail: h-kristensm @n wi. no.

and Adolescent Psychiatry.

studies suggest that SM should be conceptualized as a type of social phobia (Black and Uhde, 1995; Dummit et al., 1997; Ford et al., 1998).

The few studies addressing developmental disorder/ delay in children with SM do find a substantial propor- tion with neurobiological immaturity in speech and lan- guage, cognition, and motor function. A high frequency of enuresis is also reported (Kolvin and Fundudis, 1981; Steinhausen and Juzi, 1996). In a literature study on SM (Kristensen, 1997), 29 of 198 papers were about SM associated with developmental disordeddelay according to the abstracts. Only 2 of these studies included a con- trol group (Kolvin and Fundudis, 1981; Wilkins, 1985). The frequency of language disordeddelay is reported to be between 30% and 65% (Kolvin and Fundudis, 1981; Kurth and Schweigert, 1972; Rosler, 1981; Steinhausen and Juzi, 1996; Wilkins, 1985). Motor disordeddelay is found in 18% to 65% (Kurth and Schweigert, 1972; Rosler, 1981; Steinhausen and Juzi, 1996). The criteria for defining delay or disorder, however, vary or are not mentioned at all.

Conversely, language disorder has been reported to predict social withdrawal in girls (Benasich et al., 1993),

J . A M . A C A D . C H I L D A D O L E S C . PSYCHIATRY, 39:2 . FEBRUARY 2 0 0 0 249

KRISTENSEN

and studies of abnormal motor performance in children describe a relationship between abnormal motor perfor- mance and emotional symptoms including shyness, timidity, and social problems (Losse et al., 1991; SchafTer et al., 1985).

SM has also been reported in children with mental retardation (Klin and Volkmar, 1993), and Kolvin and Fundudis (198 1) found a lower mean IQin the SM group compared with controls.

Pervasive developmental disorder is an absolute exclusion criterion for SM in DSM-N. However, some authors have reported an association between Asperger‘s disorder and SM (Brix Andemn and Hove Thomsen, 1998; Gillberg, 1989; WolK 1995). Simons et al. (1997) reported on SM in a girl with a chromosome 18 abnormality and Hagerman et al. (1999) on a girl with SM and w e X also indicating that neurobiologid hctors may predispose for SM.

In reviewing the literature on SM to provide a basis for revisions in the DSM-IV Tancer (1992) concluded that the criteria for diagnosis have been defined very broadly so that children with diverse pathology may have been grouped together. She also stated that the paucity of well- controlled studies makes it impossible to suggest empiri- cally based changes to refine the nomenclature. One of her recommendations was a clarification of the relation- ship between specific developmental disorder and SM.

The aim of this study was to examine a group of chil- dren with SM and their matched normal controls with regard to developmental disordeddelay in language and cognition and with regard to motor function as expressed by DSM-Ndiagnoses. Comorbid anxiety disorders and elimination disorders were also assessed and diagnosed according to DSM-W.

METHOD

Subjects Subjects were recruited by mailing announcements to all 63 outpa-

tient clinics for child and adolescent psychiatry and all 278 school psy- chology services in Norway. The announcement described SM and offered treatment consultation for parents and/or therapists when partic- ipating in the study. Fulfillment of the diagnostic criteria was ascertained by telephone interview of the referring therapist. The inclusion criteria for recruitment to the study were age 3 through 17 years and f d f i h e n t of the DSM-Ncriteria for SM. Three of the children had started to talk in class to a limited degree, but they were included because of prcvious 2 to 13 years of complete silence in kindergarten or school. Children with a history of p i b k Aspergcis disorder were included. Immigrant children were excluded because of difficulties in getting a matched control group.

A total of 54 subjects (32 females and 22 males) who met the diag- nostic criteria for SM were evaluated. Of these children, 34 were referred from 24 different outpatient clinics for child and adolescent

psychiatry and 20 were referred from 20 different school psychology services in 16 of Norway’s 19 counties. For each SM child, 2 controls without SM matched for gender, age (A0 months), geographical area (same or neighboring school or kindergarten), and socioeconomic status (SES) were recruited by the teachers of the children with SM. The SES criterion, assessed by the occupations of the parents, could not always bc hlfilled because teachers sometimes did not know the parents’ occupations. The SES lcvel was rated in amrdance with the guidelines of governmental Statistics Norway. In 2-parent families the higher-rated parent occupation was used. The categories were collapsed into thc fol- lowing classcs: 1 = upper status (lawyers, physicians etc.); 2 = middle status-high (salaried employees, mean Icvel, e.g., teachers, civil senants, etc.); 3 = middle status-low (salaried employees, lower Icvel, e.g., sales clerks, etc.); and 4 = lower status (unskilled and skilled workers).

All testing and interviews of the SM and control group were per- formed by the same child and adolescent psychiatrist (the author) at the local outpatient clinic, at the childs school, or at the child’s home during a period of 2% years.

Diagnostic and Clinical Assessments

P u m t I n t m i m . The parent interview was designed for the study based on Dow and colleagu~’ (1995) recommendation for the arsess- ment of SM and Gillberg’s mommendation for the assessrncnt of chil- dren with neuropsychiatric disorders (Gillberg, 1995). The focus in the interview was on SM symptoms, previous and present treatment, somatic illnesses, family history (SM symptoms, excessive shyncss, any serious somatic illness [i.c., canccr, diabetes, rheumatoid arthritis], any psychiatric illness), risk factors in pregnancy and perinatally (Kyllerman and Hagbcrg, 1983), and dcvclopmental history with milestones and skills compared with peers. The diagnostic questions from the parent version of the Child Assessment Schedule (CAS) (Hodges et al., 1982) regarding separation anxiety, social phobia, specific phobia, ovcranx- ious disorder (generalized anxiety disorder in DSM-IU?, obsessive- compulsive disorder, enuresis, and encopresis were included in the interview. The questions in CAS were adjusted according to DSM-N criteria. In addition, the parents were presented with the questions from Gillberg’s diagnostic interview fbr Asperger’s disorder (Gillberg, 1991).

Quertionnairt. The teacher of the child completed the teacher‘s questionnaire for Asperger’s disorder (Ehlers and Gillberg, 1993).

Medical Reports. Copies of medical records from the marerniry care and the regular health checkups for the children were obtained.

Examination of the Child Because of the children’s muteness, Per- formance I Q (PIQ) was used as a measure of intelligencc. All children were assessed with the Performance section of the WISC-R (Wcchsler, 1992) or WPPSl (Wechsler, 1989). The children’s language function was evaluated with the Peabody Picture Vocabulary Tat (Dunn and Dunn, 1981), and auditory memory span (Wechsler, 1992) was eval- uated with pointing, written, or verbal response for all children. The few children who answered verbally during the assessment and the children who could respond by written language were also examined with the Verbal I Q (VIQ section of the WPPSI or WISC (Wechsler, 1989, 1992) and the Boston NamingTest (Kaplan et al., 1983). Children aged less than 6X years who did not answer verbally were also examined with the receptive part of the Reynell Developmental Language Scales (Reynell, 1977). If possible, an audiotape of a conversation at home was obtained. Motor function was assessed by age-adjusted motor tests, one ta t set for each age level 3 to 10 years and a common set from age 10 ycars and above. The sets of tests were designed for the examination on the basis of tests from Gillberg (1995), Oseretsky (1936). and Touwen (1979). Each item was scored on a scale from 0 to 4, after which the children were given a motor score (sum xore X 10 divided by number of items). The maximum score was 40.

250 J . A M . A C A D . C H I L D ADOLESC. PSYCHIATRY, 39:Z. FEBRUARY 2000

SELECTIVE M U T I S M A N D C O M O R B I D I T Y

Two of the children with SM did not want to cooperate during assessment and could not be given diagnoses which required formal testing of cognitive and language function. The motor function for 1 of those children as well as the motor function for 2 other children was evaluated by observation during play. Another child did not respond to the WPPSI but responded to the Leiter International Performance Scale (Leiter, 1979). His matched controls were also assessed by the Leiter International Performance Scale.

Assessment of Diagnoses. The following DSM-IV diagnoses were chosen to reflect developmental disorder delay: communication disor- ders (mixed receptive-expressive language disorder [ M E L D ] , expra- sive language disorder [ELD], phonological disorder [PD], and stuttering disorder), developmental coordination disorder (DCD), mild mental retardation (MMR), Asperger's disorder, and chronic tic dis- order (CTD). The exclusion criteria for SM on Asperger's disorder and communication disorder were ignored to look for comorbidity, but the exclusion criteria for the other diagnoses involved were r a p e d . The diagnoses were assessed as lifetime diagnoses except when the criteria for diagnosis required formal testing (i.e., MRELD, ELD, MMR, DCD).

The criterion for MRELD was a PIQ-VIQ split significant at the 2% level on the WISC for the older children who completed a Full Scale IQ. For the younger children who could not give a written response, Reynell results in test class 1 or 2 or a Peabody standard score <2 SD plus a difference of >20 I Q points between WPPSIl WISC PIQ and Peabody I Q or Reynell IQ qualified for a MRELD diagnosis. A diagnosis of ELD was given in the older children when they scored <2 SD on the Boston Naming Test but lacked the PIQ- V I Q split significant at the 2% level on the WISC. ELD in the younger children had to be based on a lack of PIQ-VIQ split and parental report on language skills, in addition to a tape-recording, if obtainable. The criterion for a PD diagnosis was difficulty in speech sound production beyond 5 years of age. Four children were younger than 5 years of age at the evaluation, and the pronunciation of these 5 and their matched controls was asmsed by parental report, by tape- recording, or by direct observation. A diagnosis of DCD was assigned if the child was reported to be delayed compared with peers, had a motor score <30, and obtained a PIQ >80. The Asperger diagnosis was based on the Asperger's Syndrome Diagnostic Interview, the teacher's questionnaire, and the clinical evaluation. The diagnoses of anxiety and elimination disorders were assessed according to the questions from the CAS interview. A diagnosis of stuttering disorder, CTD, MMR, Asperger's disorder, anxiety disorders, or elimination dis- orders was made if sufficient DSM-Ncriteria were present.

Statistical Methods Applied Chi-square analysis or Fisher exact tat were used to examine differ-

ences between the index group and the control group for categorical data. For continuous data, the independent t t a t was used. All p val- ues are calculated as 2-tailed, andp values less than .05 are reported as significant.

RESULTS

A total of 54 children with SM and their 108 matched controls were evaluated. The spoken language in all fam- ilies was Norwegian. All children were nonimmigrants. Two of the children with SM were siblings. Four of the children with SM including the siblings had 1 parent from abroad: 2 mothers came from the Philippines and 1 divorced father was African. The others were Caucasian.

Six of the control children had one parent from abroad, all Caucasian.

The ages of the children with SM ranged from 3.7 through 16.8 years (mean 9.0, SD 3.4). There was a pre- ponderance of female subjects (female-male ratio was 1.5:l). The mean age for the onset of SM symptoms was 3.7 years (SD 1.7), and the mean age for the first referral was 5.5 years (SD 1.8).The SES level and other back- ground data are presented in Table 1.

There was a tendency of more SM than control families in the lower SES level, but the difference was nonsignifi- cant. Other demographic factors including birth order, family size, and structure did not differentiate the groups. A history of SM in another family member was reported by approximately one fifth of the SM families, the major- ity in first-order members (the control group was not asked this question because of confidentiality).

Diagnoses Reflecting Developmental DisorderDelay

A substantial proportion of the children with SM (68.5%) met the criteria for any diagnosis reflecting devel- opmental disordeddelay compared with the control group (13.0%) (Table 2). More than 1 (2 or 3) of these diagnoses were recorded in 19 (35.2%) of the children with SM ver- sus 1 (0.9%) of the controls (x' = 36.520, df= 1,p < .OOO). The single control child who had 2 diagnoses was a boy with ELD and PD. Half of the children with SM met the DSM-IVcriteria for one or more communication dis- orders versus about one tenth of the controls, who mainly showed phonological delay.

There were significant differences between the chil- dren with SM and their controls for all single diagnostic categories reflecting developmental disordeddelay except CTD and stuttering disorder (Table 3).

Of the children with SM, 4 fulfilled the criteria for Asperger's disorder and another 4 for MMR versus none of the controls. Mean PIQ was significantly lower in the SM group even when the 4 children with MMR were excluded (96.74 [18.92] versus 106.59 [13.8]; F = 10.740, df= 76, p < .002). The children with SM also had a higher mean score on the teacher's questionnaire for Asperger's disorder (9.80 [7.05] versus 2.41 [3.65]; F = 33.12, df= 64.519,~ < BOO). Twelve (25.5%) of the children with SM versus 2 (2.1%) of the control children had a score >15 in spite of the fact that some items could not be filled in because of the children's muteness (2' = 19.9 15, df = 1, p < .OOO).

CTD was recorded in only one child in each group. However, 5 (9.3%) children with SM and 1 (0.9%) con- trol child ( p < .OO) did show some tics during assessment.

J . AM. ACAD. C H I L D ADOLESC. PSYCHIATRY. 39:'. FEBRUARY 2000 25 1

KRISTENSEN

Stuttering according to the DSM-IV criteria was not found in any of the groups, but some of the children with SM meeting a diagnosis of language disorder were reported to have problems with fluency when talking.

Elimination Disorders

Nearly one third of the children with SM met the crite- ria for any of the 2 elimination disorders compared with nearly one tenth in the control group (Tables 2 and 3). No controls were given both diagnoses versus 7 (13.0%) of the SM children ( p < .OOO).

Anxiety Disorders

Nearly three fourths of the children with SM qualified for an anxiety diagnosis versus fewer than one tenth of the controls (Table 2). The differences between the groups also reached significance in all single diagnostic categories except for specific phobia (Table 3). The most frequent anxiety diagnosis in the children with SM was social pho- bia followed by separation anxiety. Among the controls, the most frequent diagnoses were specific phobia and sep- aration anxiety. No controls met the criteria for social pho- bia, generalized anxiety disorder, or obsessivecompulsive

TABLE 1 Sociodcmographic Characteristics and Background Factors in Children With Selective Mutism (SM) and Control Children

SM (n = 54) X’IFisher Control (n = 108) na (To)b nu (To)b t Test p value

Children’s characteristics Gender

Female Male

Mcan (SD) Rcduccd optimality score pre- and perinatally‘

Mcan (SD) Physical health

>2 car infectionslyr Hospitalized Epileptic seizures

Dcvelopmcntal delay

Age (years)

Language Motor

Change of milieu No chanEe

Sociodcm~raphicslhi ly factors SES

1 (upper) 2 (middlehigh) 3 (middlelow) 4 (lower)

Illncss mother Somatic Psychiatric

Illness fatherd Somatic Psychiatric

Illncss sibling Somatic Psychiatric

Excessive shyness in family

32 22

9.0

3.9

9 16 4

28 26 18 36

8 14 19 13

11 18

5 8

2 8

39

(59.3) (40.7)

(3.4)

(2.0)

(16.7) (29.6) (7.4)

(51.9) (48.1) (33.3) (66.7)

(14.8) (25.9) (35.2) (24.1)

(20.4) (33.3)

(9.4) (15.1)

(4.0) (16.0) (72.2)

64 (59.3) 44 (40.7)

9.1 (3.4)

2.8 (1.8)

16 (14.8) 35 (32.4)

1 (0.9)

12 (11.1) 8 (7.4)

20 (18.5) 88 (81.5)

26 (24.1) 34 (31.5) 34 (31.5) 14 (13.0)

8 (7.4) 24 (22.2)

8 (7.4) 10 (9.3)

4 (3.9) 5 (4.9)

19 (17.6)

-0.259

3.769

0.095 0.129

32.134 36.033

4.663

5.843 2.314

1.219

46.744

.796

.ooo*

.750

.432

.043*

.ooo*

.000*

.036*

.198

.016*

.128

.760

.270

1 .om .030* .ooo*

NOW SES = socioeconomic status. Mcan, if indicated in the first column. SD, if indicated in the first column. n = 521104. n = 521108.

* Significant.

252 J . A M . ACAD. CHILD ADOLESC. PSYCHIATRY, 39:Z. FEBRUARY 2000

SELECTIVE MUTISM AND COMORBIDITY

TABLE 2 Groups of Diagnoses in Children With Sclcctive Mutism (SM) and Control Children

Diagnosis (DSM-IV)

X'IFisher SM (n = 54) Control (n = 108) n (%I n (%I Tat p value

Any diagnosis Any dcvclopmental disorder Any elimination disorder Any anxiety disorder Any communication disorder" No. of diagnoxs

1 2 3-7

Diagnosis in 2 Groups 3 Groups

Anxiety disorder and developmental disorder

53 (98.1) 37 (68.5) 17 (31.5) 40 (74.1) 26 (50.0)

10 (18.5) 13 (24.1) 30 (55.4)

32 (59.3) 9 (16.7)

25 (46.3)

28 (25.9) 14 (13.0) 10 (9.3) 8 (7.4)

12 (11.5)

24 (22.2) 3 (2.8) 1 (0.9)

3 (2.8) 0 (0.0) 1 (0.9)

75.111 51.510 12.800 76.737 27.832

110.467

67.807

55.000

.mo*

.000'

.ooo*

.ooo*

.om*

.000*

.om*

.ooo*

.000*

" n = 521104. Significant.

disorder. Of the children with SM, 37.1% received from 2 to 4 of the anxiety diagnoses versus none of the controls (2' = 81.023, df= 2,p < .OOO).

Multiple Diagnoses: Cornorbidity

All children with SM but one met the criteria for any of the 15 diagnoses in question compared with one fourth of the control children (Table 2). As many as 43 (79.5%) of the children with SM fulfilled more than one

diagnosis compared with 4 (3.7%) in the control group (x' = 109.323, df = 2, p < .OOO).

Nearly half of the children with SM qualified for a diagnosis in both the anxiety and the developmental cat- egory versus only one of the controls. Of the 5 1 children given a developmental diagnosis, an additional anxiety diagnosis was assigned in 25 (67.7%) of the children with SM but only in 1 (7.1%) of the controls (x' = 14.839, df= 1,p < .OOO).

TABLE 3 Comorbid Conditions in Children With Sclcctive Mutism (SM) and Control Children

X'IFishcr Diagnosis SM (n = 54) Control (n = 108) (DSM-N) n (%I n (Yo) Tut D Value

Mixed rcceptivc-expressive language disorder" Expressive language disorder" Phonological disorder Stuttering disorder Dcvclopmental coordination disorderb Chronic motor tic disorder Mild mental retardation" Aspergcr's disorder Enuresis Encopresis Scparation anxiety Spccific phobia Social phobia Gencralizcd anxiety disorder Obsessive-compulsive disorder

9 (17.3) 6 (11.5)

23 (42.6) 0 (0.0) 9 (17.0) 1 (1.9) 4 (7.7) 4 (7.4)

16 (29.6) 8 (14.8)

17 (31.5) 7 (13.0)

36 (67.9) 7 (13.0) 5 (9.3)

1 (1.0) 1 (1.0)

11 (10.2) 0 (0.0) 1 (0.9) 1 (0.9) 0 (0.0) 0 (0.0) 8 (7.4) 2 (1.9) 3 (2.8) 5 (4.6) 0 (0.0) 0 (0.0) 0 (0.0)

.001*

.OM* 22.800 .001*

37.723 .000* 1 .000 .011* ,011'

14.087 .ooo* .#3*

27.409 .#Of .lo7 .om* .om* .004*

a n = 521104. n = 531106.

* Significant.

J . AM. ACAD. CHILD ADOLESC. PSYCHIATRY, 3 9 : 2 , FEBRUARY 2000 253

KRISTENSEN

Excluding the 4 children with a diagnosis of Asperger's disorder and their 8 controls from the study did not change any of the significant group differences except for specific phobia, where the exclusion of one control child changed the difference from nonsignificant to just signif- icant ( p < .043).

DISCUSSION

No previous study on SM and comorbidity has in- cluded a comprehensive clinical assessment based on a battery of standardized tests in both children with SM and their matched controls combined with a diagnostic interview of the children's parents. Considering the low prevalence of SM, the present sample must be regarded as reasonably large.

SM and Comorbidity With Developmental Disorder/Delay

A high proportion of children with SM (68.5%) had developmental disordeddelay. Comparable studies using DSM-Ncriteria are lacking. The 50% of children with SM with communication disorder is in line with the 30% to 65% language disordeddelay recorded by other authors (Kolvin and Fundudis, 1981; Rosler, 1981; Steinhausen and Juzi, 1996; Wilkins, 1985). In contrast, 2 studies on SM focusing on anxiety disorders, using rating scales and diagnostic interviews, found only 10% (Black and Uhde, 1995) and 11% (Dummit el al., 1997) with language disordeddelay. However, they used no test battery.

Seventeen percent of the children with SM met the criteria for a DCD diagnosis, but nearly half of the chil- dren had a history of motor delay. Possible explanations include motor sofi signs abating with time (Gillberg et al., 1989), poor sensitivity of the test battery used, and too strict diagnostic criteria applied. Only 2 studies have pre- viously evaluated motor function in children with SM directly (Kurth and Schweigert, 1972; Rosler, 1981). They report on abnormal motor function in up to 65.5% of their sample, supporting a view of frequent minor motor problems in children with SM.

MMR, primarily unrecognized, was revealed in 4 (7.8%) of the children with SM. Three of them were 9 to 14 years old, indicating that cognitive problems may be undiagnosed in SM as noted by Klin and Volkmar (1993) and Wright (1968).

The Asperger diagnosis recorded in 4 (7.4%) other chil- dren with SM was also previously unknown. This rate is high compared to a population prevalence of 0.3%

(Gillberg, 1995). SM is reported in a close relative in 2 of 23 children with Asperger's disorder (Gillberg, 1989) and in 9.2% of schizoid children (WON, 1995); Brix Andersson and Hove Thomsen (1998) described 3 (8.1%) SM chil- dren who met the criteria for both SM and atypical Asper- gets disorder in their retrospective study. Combined, this indicates a relationship between the conditions and lends support to Wolffs (1995) suggestion that a diagnosis of schizoid/Asperger disorder needs to be considered in all children with SM. The proportion of children with SM with a score higher than 15 on the teacher's Asperger ques- tionnaire also raises an interesting question of empathy skills among children with SM. Unfortunately, this study did not address this question in more detail.

Elimination Disorders

Previous estimates of the prevalence of enuresis in chil- dren with SM vary from 4% to 42% (Black and Uhde, 1995; Dummit et al., 1997; Kolvin and Fundudis, 1981; Steinhausen and Juzi, 1996) and for encopresis from 7% (Black and Uhde, 1995) to 17% (Kolvin and Fundudis, 1981). Developmental delays are common in children with enuresis (Mimouni et al., 1985; Steinhausen and Gobel, 1989), and the high percentage of enuresis (29.6%) in this study may be regarded as another indicator of the connec- tion between SM and developmental immaturity. For encopresis this connection seems less clear (Hersov, 1994).

Anxiety Disorders

Anxiety disorders were the most common recorded diagnoses in the SM children in this study, in agreement with previous studies (Black and Uhde, 1995; Dummit et al., 1997; Steinhausen and Juzi, 1996). The rate of social phobia (66.7%) was somewhat less frequent than that reported by Black and Uhde (1995) and Dummit et al. (1997). They focused primarily on SM and anxiety symp- toms, and they used more sophisticated methods and spe- cial assessment of ambiguous cases.

Multiple Diagnoses: Comorbidity

The symptom burden of children with SM is reflected by the high proportion with more than one of the diag- noses chosen in the study (79.5% had more than 1 and 55.4% had from 3 to 7 diagnoses). In the SM children with developmental disorder, the substantial comorbidity with anxiety disorders seems fir more fiequent than comor- bidity with anxiety in children with neurological sofi signs or in children with communication disorders (Cantwell

254 J . AM. ACAD. CHILD ADOLESC. PSYCHIATRY. 39:2 . FEBRUARY 2000

SELECTIVE M U T I S M A N D COMORBIDITY

and Baker, 1987; Gillberg, 1995) and can thus hardly be explained by the developmental problems alone. Nearly three fourths of the SM group reported excessive shyness in their immediate families, indicating that familial tem- peramental hctors may be of influence. The figures in this study correspond well to findings of the few previous studies addressing this question (Black and Uhde, 1995; Brown and Lloyd, 1975; Steinhausen and Adamek, 1997).

Sociodemographic and Background Factors

The female-male ratio in this study, 1.5:1, is within the range reported in previous studies: 1.1 : 1 (Kolvin and Fundudis, 1981) to 2.4:l (Wright, 1968). The SM group had significantly more frequent moves and/or changes of kindergarten or school, indicating a potential risk factor in the development of mute behavior. The significantly higher “reduced optimality score” in pregnancy and peri- natally is in line with their high rate of developmental disordeddelay (Gillberg, 1995).

SM symptoms are often explained in the light of reported psychiatric illness in the parents and/or family discord (Tancer, 1992). The tendency of more frequent psychiatric illness in the parents of children with SM did not reach significance in the study and should indicate the need for caution in relating the cause of the SM symptom directly to psychiatric problems in the parents.

Limitations

The children with SM in this study come from a clin- ical sample and therefore might have more severe symp- toms than children with SM in the general population. However, most children with SM symptoms will first be referred to the school psychology counseling service, entry level in the professional helping services in Norway. In the sample, 27.8% of the children with SM had been in contact with this service only

This study was open because the nature of muteness makes blinding impossible. All evaluations and inter- views were performed by a single child and adolescent psychiatrist (the author), experienced in neuropsychiatric testing. While this might increase validity, it also makes the study prone to investigator bias. However, reinvesti- gation by another clinician was financially and practically beyond reach as the children came from all over Norway Use of standardized tests and confirmation of clinical findings by parent interview should reduce bias. The large group differences found can hardly be explained by investigator bias only.

Retrospective interviews concerning specific dates for developmental milestones may have low validity. How- ever, asking about overall development compared with peers should give more reliable answers (Gillberg, 1995). Validation by medical records and the use of a control group also reduces this problem.

The selection of diagnoses may have left some comor- bid symptoms undiagnosed. However, adding the entire CAS and an SM child interview would make the total pro- cedure too time-consuming for single-session assessment.

Despite these shortcomings, this study has method- ological advantages in that it uses a nationwide, fairly large sample, a matched control group, and a direct stan- dardized assessment of the children.

Clinical Implications

SM children’s mutism and their avoidant behavior are often misinterpreted. Mutism in communication is pro- vocative, and the children are often regarded as controlling and manipulating instead of shy and anxious. Their mutism may also conceal a developmental problem and result in demands not adjusted to their developmental level. Diagnostic investigations should therefore focus both on anxious psychopathology and possible developmental disordeddelay in children with SM. Assessment of cogni- tive function is essential. A possible diagnosis of Asperger‘s disorder needs also to be considered. Therapeutic interven- tions should focus on alleviating the anxiety symptoms and adapting demands to the a d level of functioning if any developmental problems exist.

Conclusions

This study describes comorbidity between SM and developmental disorder/delay occurring nearly as fre- quently as between SM and anxiety disorders. Elimina- tion disorders are also associated with SM, although less frequently. A combination of developmental and anxiety diagnoses is often found. Many authors share the view that SM is a condition with a multifactorial etiology (Kolvin and Fundudis, 1981; Tancer, 1992). The present study gives support to this view and also indicates that SM should be regarded as a symptom of anxiety, reflect- ing different underlying vulnerabilities, rather than a distinct disorder. An interesting question to address is how the biologically determined immaturity influences the development of the mute behavior. Children with imma- ture function in one or more areas are ofien met by demands not adjusted to their functional level. The common

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denominator may be that their neurodevelopmental immaturity makes these children more vulnerable to “everyday traumas” and that they tend to react to nov- elty with anxiety and withdrawal. The prevalence of excessive shyness in other family members may indicate genetic factors in the development of the symptom, and one may ask whether the developmental immaturity also may be of genetic origin. The presence of genetic factors remains speculative and is an area for future research, along with the need for a better understanding of the factors that may strengthen or resolve the mutism when first established.

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