Chapter 1

General Concepts of Disease:

Principles of Diagnosis

Learning Objectives

• Define: – Disease– Lesions– Organic and functional disease– Symptomatic and asymptomatic disease– Etiology– Pathogenesis

• Categories of human disease• Types of diagnostic tests and procedures

Characteristics of Disease (1 of 3)

• Disease: disturbance of body structure or function

• Lesions: well-defined, characteristic structural changes in organs and tissues as a result of disease

• Organic disease– Associated with structural changes– Gross examination– Histologic examination

• Functional disease– No morphological abnormalities yet body functions

are profoundly disturbed

Characteristics of Disease (2 of 3)

• Pathology: study of disease– Pathologist: physician who specializes in diagnosing

and classifying diseases by studying the morphology of cells and tissues

– Clinician: physician/health care professional that cares for patients

• Symptoms: subjective manifestations such as pain or weakness

• Signs: physical findings or objective manifestations such as swelling or redness

Characteristics of Disease (3 of 3)• Symptomatic disease: with symptoms and/or signs• Asymptomatic disease: no signs or symptoms

– Distinction between asymptomatic and symptomatic depends on extent

– Early stages of disease, usually asymptomatic– If not treated, progresses to symptomatic

• Etiology: cause of disease• Etiologic agent: agent responsible for causing

disease• Pathogenesis: process of development of disease • Pathogen: any microorganism that causes disease

Classifications of Disease (1 of 3)

• Congenital and hereditary diseases– Developmental disturbances– Causes: genetic abnormalities; abnormalities

in chromosome number or distribution; intrauterine injury; interaction of genetic and environmental factors

– Hemophilia (hereditary), German measles (congenital)

Classifications of Disease (2 of 3)

• Inflammatory diseases: Body reacts to injury through an inflammatory process– Bacteria or microbiologic agents: sore throat– Allergic reaction: hay fever– Autoimmune diseases: SLE, diabetes type 1– Unknown etiology

• Degenerative diseases– Tissue or organ degeneration as a result of aging or

breakdown– Arthritis, atherosclerosis

Classifications of Disease (3 of 3)• Metabolic diseases: Disturbance in metabolic

process in body– Diabetes, hyper- or hypothyroidism, fluid and electrolyte

imbalance• Neoplastic diseases: Uncontrolled cell growth

– Benign: lipoma– Malignant: Lung cancer

• Basis of classification– 1. Similarity of lesions– 2. Similarity of pathogenesis

• Diseases with similarities may not necessarily be closely related

Health and Disease– WHO (1948) – wellness is the complete state of

physical, mental and social well-being and not simply the absence of disease and infirmity.

– Good health: more than the absence of disease– Condition in which body and mind function

efficiently and harmoniously as an integrated unit

• Traditional medicine: goal is to cure or ameliorate disease.

• Modern medicine: advances relieve suffering and advance human welfare but do not guarantee good health.

• Allopathic medicine- usually refers to traditional western medicine -

• The term allopathy was coined by the founder of homeopathy, Samuel Hahnemann, to differentiate homeopathic practices from conventional medicine of the day, based on the types of treatments used. Hahnemann used allopathy to refer to what he saw as a system of medicine that combats disease by using remedies that produce effects in a healthy subject that are different (hence Greek root allo- "different") from the effects produced by the disease to be treated.

• Contrast to Homeopathic medicine• Preventive medicine• Pharmaceutical • Neutraceutical

• Homeopathy is a form of alternative medicine in which practitioners use highly diluted preparations. Homeopathy was first proposed by German physician Samuel Hahnemann in 1796, based on an ipse dixit axiom formulated by Hahnemann, which he called the law of similars, preparations which cause certain symptoms in healthy individuals are given to patients who already exhibit similar symptoms.

• Preventive medicine or preventive care refers to measures taken to prevent diseases, (or injuries) rather than curing them or treating their symptoms. The term contrasts in method with curative and palliative medicine, and in scope with public health methods (which work at the level of population health rather than individual health).

• A pharmaceutical drug, also referred to as medicine or medication, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease

• Nutraceutical, a term combining the words “nutrition” and “pharmaceutical”, is a food or food product that provides health and medical benefits, including the prevention and treatment of disease.

• Nutraceutical products may range from isolated nutrients, dietary supplements and specific diets to genetically engineered foods, herbal products, and processed foods such as cereals, soups, and beverages

Continuum of Health and Disease

Good Health Serious Illness

• Everyone is somewhere between the midpoint and good health

• Good health requires active participation, assuming responsibility for one’s health– Eat properly, exercise, avoid harmful excesses

such as overeating, smoking, heavy drinking, or using drugs

– Use one’s mind constructively, express emotions appropriately, nurture a positive mental attitude

Principles of Diagnosis

• Diagnosis: determination of nature and cause of illness– Clinical history– Physical examination– Differential diagnosis

• Prognosis: eventual outcome of disease• Treatment

– Specific treatment – directed at underlying cause– Symptomatic treatment – alleviates symptoms but

does not influence course of disease

Clinical History (1 of 2)

• 1. History of current illness– Severity, time of onset, and character of

patient’s symptoms• 2. Medical history

– Details of general health and previous illnesses that may shed light on current problems

• 3. Family history– Health of patient’s parents and family

members; diseases that run in families

Clinical History (2 of 2)

• 4. Social history– Patient’s occupation, habits, alcohol and

tobacco consumption, general health, current problems

• 5. Review of symptoms– Symptoms other than disclosed in history of

present illness, suggesting other parts of the body affected by disease

Physical Examination

• Physical examination– Systematic examination of patient, with emphasis on

parts of body affected by illness– Abnormalities noted correlated with clinical history

• Differential diagnosis– Consideration of various diseases or conditions that

may also explain patient’s symptoms and signs– Diagnostic possibilities narrowed by selected

laboratory tests or other diagnostic procedures– Opinion of medical consultant may be sought

Screening Tests

• Screening tests for detection of disease– Detect early asymptomatic diseases amenable to

treatment to prevent or minimize late-stage organ damage

• Screening for some genetic diseases– To screen for carriers of some genetic diseases

transmitted from parent to child as either dominant or recessive trait

– Identifying carriers allows affected persons to make decisions on future childbearing or management of current pregnancy

– Example: recessive gene for sickle cell anemia in 8% of Black population

Requirements for Effective Screening

• A significant number of persons must be at risk for the disease in the group being screened.

• A relatively inexpensive noninvasive test must be available to screen for the disease that does not yield a high number of false-positive or false-negative results

• Early identification and treatment of the disease will favorably influence course of disease.

Examples of Screening Tests• PPD - For TB• PSA – Prostate Specific Antigen – For Prostate Cancer• Alpha Fetoprotein – screening to detect certain fetal

abnormalities• Mammogram and BRAC to detect breast cancer• Pap Smear for cervical cancer• Colonoscopy for Colon Cancer• Blood Sugar test for diabetes• Blood Pressure Determination for Hypertension

Diagnostic Tests and Procedures (1 of 13)

• Clinical laboratory tests– Purpose: To determine concentration of substances in

blood or urine frequently altered by disease– Uses:

• Determine concentration or activity of enzymes in the blood

• Evaluate function of organs• Monitor response of certain cancers to treatment• Detect disease-producing organisms in urine,

blood, feces• Determine response to antibiotics

Lab Tests

Lab Tests

Lab Tests

Diagnostic Tests and Procedures (2 of 13)

• Tests of electrical activity: to measure electrical impulses associated with bodily functions and activities– ECG: measures serial changes in electrical activity of

the heart in various phases of the cardiac cycle• Identify disturbances in heart rate, rhythm, abnormal

impulses• Recognize heart muscle injury from ECG abnormalities

– EEG: measures electrical activity of brain; brain waves

– EMG: measures electrical activity of skeletal muscle during contraction and at rest

Diagnostic Tests and Procedures (3 of 13)

• Radioisotope (radionuclide) studies: evaluate organ function by determining rate of uptake and excretion of substances labeled with a radioisotope

• Uses:– Anemia: radioisotope-labeled vitamin B12– Hyperthyroidism: radioactive iodine– Pulmonary blood flow: albumin; to detect presence of

blood clots– Cancer spread: phosphorus; to determine presence of

tumor deposits in bone or spine– Heart muscle damage: evaluate blood flow

Diagnostic Tests and Procedures (4 of 13)

• Endoscopy– To examine interior of body using rigid or flexible

tubular instruments equipped with lens and light source

– To perform surgery formerly done through large abdominal incisions• Bronchoscope: trachea and major bronchi• Cystoscope: bladder• Laparoscope: abdomen

• Ultrasound– Mapping echoes produced by high-frequency sound

waves transmitted into body; echoes reflect change in tissue density, producing images

Diagnostic Tests and Procedures (5 of 13)

• X-ray– Principle: use of high-energy radiation waves at lower

doses to produce images to help diagnose disease– Can penetrate through tissues at varying degrees

depending on tissue density – Act on a photographic film or plate (roentgenogram)

as the rays leave the body• Radiopaque: appears white on film; high-density

tissues such as bone absorb most of the rays • Radiolucent: appears dark on film; low-density

tissues allow rays to pass through

Diagnostic Tests and Procedures (6 of 13)

• X-ray can include use of contrast media to outline structures not otherwise visualized on standard films– Barium sulfate: intestinal tract – Radiopaque oil: bronchogram– Intravenous dye: intravenous pyelogram; urinary tract– Radiopaque tablets: visualize gallstones– Arteriogram: visualize blood flow, identfy narrowing or

obstruction– Cardiac catherization: blood flow through heart, detect

abnormal communications between chambers

Diagnostic Tests and Procedures (7 of 13)

• Computed tomographic (CT) scans– Principle: radiation detectors record amount of X-rays

or ionizing radiation absorbed by body and feed data into a computer that reconstructs the data into an image

– Radiopaque and radiolucent tissues appear white and dark as in a conventional x-ray

– Individual organs sharply demarcated by planes of fat that appear dark because of its low density

– Delivers higher dose of ionizing radiation than x-ray

Diagnostic Tests and Procedures (8 of 13)

• Uses of computed tomographic (CT) scans– Cancer screening asymptomatic individuals– Detect abnormalities in internal organs that

cannot otherwise be identified by standard x-ray

Diagnostic Tests and Procedures (9 of 13)

• Magnetic resonance imaging (MRI)– Principle: computer-constructed images of body

based on response of hydrogen protons in water molecules when placed in a strong magnetic field• Protons align in the direction of the magnetic field• Protons are temporarily dislodged and wobble when

radiofrequency waves are directed at them• Protons emit a measurable signal (resonance) that can be

used to construct images• Intensity of resonance depends on water content of tissues,

strength and duration of radiofrequency pulse

Diagnostic Tests and Procedures (10 of 13)

• MRI: advantages over CT scan– Does not use ionizing radiation– Can detect abnormalities in tissues surrounded by

bone, such as spinal cord, orbit, skull– Bone interferes with scanning because of its density

but does not produce an image in MRI because of its low water content

• Uses– Multiple sclerosis– Superior to mammography in detecting breast cancer

Diagnostic Tests and Procedures (11 of 13)

• Positron emission tomography (PET)– Principle: Measures metabolism of

biochemical compounds that are labeled with positron-emitting isotopes to measure organ function, example glucose

– Disadvantages• Very expensive and not widely available• Requires facilities for incorporating the isotopes

into the biochemical compound

Diagnostic Tests and Procedures (12 of 13)

• Uses of PET– Assess biochemical functions in brain– Determine metabolic activities of organ or

tissue; specific site in an organ where compound is metabolized

– Evaluate changes in blood flow in heart muscle following a heart attack

– Distinguish benign from a malignant tumor (increased glucose uptake in malignant versus benign tumors)

Diagnostic Tests and Procedures (13 of 13)

• Cytologic and histologic examinations– Papanicolau (Pap) smear: identifies abnormal

cells in fluids or secretions; for recognizing early changes that may be associated with cervical and other cancers

– Biopsy: tissue samples obtained for histologic examination to determine abnormal structural and cellular patterns accompanying disease• Liver, kidney, bone marrow

Radioisotope bone scan of head, chest, and pelvis © Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

Ultrasound examination of 22-week-old fetus

Courtesy of Belinda Thresher

X-ray of colon with radiopaque barium sulfate© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

Bronchogram showing normal caliber and branching of bronchi and bronchioles

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

IVP showing large cyst, right kidney

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

X-ray of gallbladder; gallstones appear as radiolucent (dark) within a radiopaque bile (white)

Opened gallbladder, same patient

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

Carotid angiogram, narrowing of carotid artery© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

Computed tomographic scan, CT scan

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

CT scan, chest, white nodule on left lung indicates tumor

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

CT scan, abdomen at level of kidneys, fluid-filled cysts, right kidney

© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

MRI, brain, with malformation within brain stem© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School

Discussion

• What are the underlying principles for these diagnostic procedures: x-ray, CT scan, MRI, PET?

• Explain the requirements for an effective screening.

• Differentiate:– Symptomatic versus specific treatment– Sign versus symptom– Symptomatic versus asymptomatic disease– Diagnosis versus prognosis