Role of the Surgical Pathologist in Diagnosis of Drug-induced Liver Injury: Recognizing Specific Patterns of Drug Injury.

Eighteen histologic patterns of drug-induced liver injury (DILI) are described, most of which are also seen in other commonly occurring acute and chronic liver diseases. However, certain patterns such as sinusoidal obstruction syndrome/veno-occlusive disease, "bland" cholestasis and cholestatic hepatitis are more often caused by drugs than other competing etiologies. Amiodarone, acetaminophen, anabolic androgenic steroids and estrogens, result in histologic patterns that are virtually diagnostic of the respective drug. Recognition of a DILI or drug specific injury pattern enables the clinician to focus on eliciting an appropriate history to identify the offending agent, which may otherwise be rare and not immediately apparent. Although drugs can mimic any and every liver disease, the mimicry is often imperfect. Unusual features that do not completely fit the clinicopathologic paradigm of the mimicked liver disease are clues to diagnosis of DILI. When mimicking a liver disease, drugs tend to hasten or accelerate the natural progression of the disease. Novel immunomodulatory drugs for inflammatory disorders and cancer may cause unintended effects on the immune system, resulting in immune-related side effects. The role of the pathologist in diagnosis of DILI is to recognize known patterns of DILI, and either confirm a diagnosis when clinically suspected, or alert the clinician to the possibility of DILI when it is not suspected. The latter is particularly vital in contemporary practice, which is witnessing an accelerated pace of drug development, and a surge in consumption of nutritional supplements and herbal compounds by an increasingly health conscious society.