Disease

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Disease: definition and clinical examples

Definition

Any deviation from or interruption of normal structure or function of a body part/organ/system, manifested by characteristic signs and symptoms, with etiology/pathology/prognosis possibly known or unknown.

Disease vs health

• Health = normal structure/function and ability to maintain homeostasis.
• Disease = disturbance of homeostasis due to underlying abnormal process.

Core components of a disease

1. Etiology (cause)
2. Pathogenesis (mechanistic steps from cause → disease/how the disease develops)
3. Pathophysiology (how normal function is disturbed/functional consequences of a disease process)
4. Morphologic changes (structural changes, if applicable)
5. Clinical manifestations (symptoms + signs)
6. Outcome (recovery, chronicity, complications, death)

Disease vs related terms

• Symptom = subjective complaint (patient-reported).
• Sign = objective finding (clinician/test).
• Syndrome = cluster of signs/symptoms that occur together.
• Etiology = cause of disease.
• Pathogenesis = sequence of events from cause → disease.
• Pathophysiology = functional disturbance produced by disease.

Examples

Example 1: Acute appendicitis

• Etiology: luminal obstruction (fecalith/lymphoid hyperplasia)
• Pathogenesis: obstruction → bacterial overgrowth → inflammation → ischemia/perforation
• Pathophysiology: visceral pain then parietal irritation
• Clinical: abdominal pain migration + nausea (symptoms), fever + rebound tenderness (signs)

Example 2: Type 1 diabetes mellitus

• Etiology: autoimmune β-cell destruction (genetic + environmental triggers)
• Pathogenesis: immune-mediated β-cell loss → insulin deficiency
• Pathophysiology: impaired glucose uptake + increased lipolysis/ketogenesis
• Clinical: polyuria/polydipsia/weight loss; DKA risk

Example 3: Atherosclerosis

• Etiology: multifactorial (LDL, hypertension, smoking, diabetes)
• Pathogenesis: endothelial dysfunction → LDL oxidation → foam cells → plaque → rupture
• Pathophysiology: reduced perfusion + thrombosis
• Clinical: angina, TIA/stroke, claudication

Diagram

Etiology → Pathogenesis → Pathophysiology → Symptoms/Signs → Complications/Outcome

Bibliography

• KUMAR, Vinay; ABBAS, Abul K.; ASTER, Jon C. Robbins & Cotran Pathologic Basis of Disease. 10th edition. Philadelphia: Elsevier, 2021. ISBN 978-0-323-60992-0.
• HALL, John E. Guyton and Hall Textbook of Medical Physiology. 14th edition. Philadelphia: Elsevier, 2020. ISBN 978-0-323-67280-1.
• DORLAND. Dorland’s Illustrated Medical Dictionary. 32nd edition. Philadelphia: Saunders/Elsevier, 2011. ISBN 978-1-4160-6257-8.