etiology

Broad etiological categories used in clinical reasoning include genetic, infectious, immunologic, neoplastic, metabolic, toxic, traumatic, vascular, degenerative, and idiopathic, the last meaning no cause has been identified. The distinction from pathogenesis matters because interventions differ: in tuberculosis the etiology is Mycobacterium tuberculosis and treatment is antimycobacterial, while the pathogenesis is a type IV hypersensitivity granulomatous response that itself may need corticosteroids in tuberculous meningitis or pericarditis. Establishing etiology for an infectious agent classically invokes Koch's postulates, while for non-infectious disease the Bradford Hill criteria (strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, analogy) are used to argue that an observed association is causal. Temporality, that the exposure precedes the outcome, is the only criterion that is strictly necessary.