Whipple disease

Pathophysiology: Tropheryma whipplei is a gram-positive, PAS-positive, rod-shaped actinomycete that infects macrophages, primarily in the small intestine, leading to impaired lymphatic transport and malabsorption. The organism is difficult to culture and is often identified via PCR or characteristic histology.

Clinical features: The disease has a classic tetrad—arthralgias (often the earliest symptom, migratory and affecting large joints), diarrhea, abdominal pain, and weight loss due to malabsorption. Other systemic manifestations include lymphadenopathy, low-grade fever, hyperpigmentation, and neurologic symptoms (dementia, ophthalmoplegia, myoclonus—classically oculomasticatory myorhythmia) and cardiac involvement (culture-negative endocarditis). CNS involvement can occur even without GI symptoms and requires prolonged treatment to prevent relapse.

Diagnosis: Small bowel biopsy shows PAS-positive, foamy macrophages packed with the bacilli in the lamina propria, often with villous blunting. Electron microscopy or PCR for T. whipplei DNA can confirm diagnosis, especially in atypical presentations (e.g., isolated CNS or cardiac disease). PAS-positive macrophages must be differentiated from Mycobacterium avium complex (MAC) infection, which also causes PAS-positive macrophages in the small intestine (differentiated by acid-fast staining, positive in MAC, negative in Whipple disease).

Treatment: Long-term antibiotic therapy is required due to the ability of the organism to persist intracellularly and cause CNS relapse. Typical regimens include initial IV ceftriaxone or penicillin for 2 weeks, followed by prolonged oral trimethoprim-sulfamethoxazole (TMP-SMX) for 1–2 years to ensure CNS penetration and eradication.

Clinical significance: Whipple disease is a classic USMLE topic due to its unique organism, characteristic biopsy findings, and multisystem involvement mimicking other malabsorptive or rheumatologic diseases. It should be considered in patients with unexplained arthralgias, weight loss, and diarrhea, especially with neurologic or cardiac symptoms.