Leptospirosis is a zoonosis transmitted by Leptospira , known for its immunomodulatory activity capable of stimulating immune activation and triggering autoimmune diseases, including polymyositis. This report describes the diagnosis of polymyositis confirmed by muscle biopsy in a patient who developed symptoms after confirmed leptospirosis. A 48-year-old male farmer, previously healthy, reported myalgia and muscle weakness for 2 months, predominantly in upper limbs and back, with difficulty walking, asthenia, headache, oliguria, and chills. Initial evaluation revealed elevated CPK and liver enzymes, raising suspicion for leptospirosis, later confirmed by serology and treated with ampicillin–sulbactam and doxycycline. Despite treatment, myalgia persisted, progressing to moderate dysphagia, weight loss, and reduced strength (shoulder girdle grade 3, pelvic girdle grade 4), without cutaneous changes. An inflammatory myopathy was suspected, and the following laboratory tests were ordered: CPK 874; aldolase 15 (<7.6); AST 81; ALT 134; ANA non-reactive; anti-Jo-1 non-reactive; CRP <0.6; ESR 10; creatinine 0.7; urea 28; TSH 0.337; viral serologies (HIV, HCV, HBV, syphilis, CMV, HTLV) negative. Deltoid biopsy revealed lymphocytic endomysial and perimysial infiltrate, immunohistochemistry positive for CD3, CD4, CD8, confirming polymyositis. Treatment with prednisone and azathioprine produced significant clinical improvement. This case illustrates diagnostic complexity at the intersection of infectious diseases and inflammatory myopathies. Leptospirosis should be considered in patients with intense myalgia and high CPK, especially with environmental exposure. However, persistent weakness after infection should prompt investigation of alternative diagnoses such as polymyositis. Muscle biopsy is the gold standard, and treatment response is clinically informative. The relationship between leptospirosis and polymyositis is poorly understood and warrants further investigation to clarify possible shared pathogenic mechanisms.
Menezes et al. (Sun,) studied this question.