Hirayama Disease
Hirayama Disease
Aka Juvenile Muscular Atrophy of the Distal Upper Extremity
Rare disease that affects predominantly males in their 2nd or early 3rd decade of life
Features include muscular weakness and atrophy in the hand and forearm
Brachioradialis muscle is spared, therefore the pattern of forearm involvement is referred to as an oblique amyotrophy
Unilateral involvement vs asymmetric and symmetric bilateral involvement
Hirayama Disease
Insidious onset and clinical course is steadily progressive
After a period of initial deterioration, a stable stage is reached
Pathogenesis is constantly debated.
Dynamic compression of the spinal cord felt to be an important finding in the diagnosis
Hirayama Disease: Pathogenesis
Dynamic cord compression during neck flexion with forward displacement of the posterior dura is an unequivocal finding in the progressive stage
However, this finding is absent in older patients who have reached a stable stage
Some believe that a disproportional length between the vertebral column and the dural canal leads to a “tight” dural canal.
Hirayama Disease: Pathogenesis
The normal cervical dura is slack and consists of transverse folds during neck extension.
With flexion, the length of the cervical canal increases
In normal patients, the dural slack compensates for the increased length in flexion
Patients with Hirayama dz may have an imbalance in growth of vertebrae and dura, and the short dural canal cannot compensate; therefore, the dural canal becomes tight when the neck is flexed. Results in an anterior shift of the posterior dural wall,
causing spinal cord compression
Hirayama Disease: Pathogenesis
The pathogenesis of cervical myelopathy may be ischemic changes or chronic trauma with repeated neck flexion. Compression may cause microcirculatory disturbances in
anterior portion of the cord, leading to necrosis of anterior horns
Changes are often greatest at C6 vertebral level
Primarily affects the anterior horn cells, and in later stages of the disease, spinal cord atrophy ensues.
Some autopsy studies report ischemic changes in the anterior horn cells, with asymmetric cord thinning.
Hirayama Disease: MR findings
Flexion-extension images demonstrate forward migration of the posterior wall of dura
Posterior epidural space enlarges with flexion and is seen as a crescent of high signal on T1 and T2 images Likely reflects congestion of posterior internal vertebral
venous plexus
Uniform enhancement of epidural space with contrast
May have flow voids in epidural space
Compressive flattening of the spinal cord with forward shifting of the posterior dura.
Hirayama Disease: MR findings
Spinal cord flattening is asymmetric in majority of cases. This is an important finding on routine nonflexion MR
images and should raise the suspicion.
Spinal cord atrophy limited to the anterior horn cells found in later stages of the disease.
Morphologic changes on MR images correlate well with clinical and electromyographic data
Hirayama Disease
Two flexion T1 post Gd images show increase thickening of posterior epidural space (arrows) which enhances and
contains flow voids.
Hirayama Disease
Axial T1 post Gd images in same patient show thick epidural space, particularly posteriorly, compressing the
spinal cord.
Hirayama Disease: Treatment
Avoidance of neck flexion can stop the progression of the disease
Some advocate application of a cervical collar for 3 to 4 years since the progressive stage usually ceases in a few years.
Surgical intervention, including cervical decompression and/or fusion with or without duraplasty, may be an option.