Caseous, Necrotic Material and Epithelioid Cell Granulomas in Synovial Fluid from a Patient with Tuberculous Infection

BACKGROUND: The gross appearance and cytologic findings in synovial fluid in tuberculous infections are similar to those in other types of chronic synovial effusion. Demonstration of acid-fast bacilli (AFB) is required for a definitive diagnosis of tuberculous effusion; it is reported in only 20% of cases. The presence of frank caseous necrotic material and epithelioid cell granulomas in synovial fluid samples is unusual but strongly indicative of tuberculous infection. CASE: A 28-year-old man, on treatment for pulmonary tuberculosis, presented with a history of right ankle swelling, which was clinically interpreted as nonspecific synovitis. The synovial fluid was yellowish, with fluffy, whitish material. Cytologic smears showed abundant, caseous, necrotic material; a few histiocytic aggregates; and occasional epithelioid cell granulomas. Although stain for AFB was negative, considering the clinical presentation, a diagnosis of tuberculous synovitis could be rendered. CONCLUSION: Caseous, necrotic material and epithelioid granulomas in synovial fluid are highly unusual but, when present, can be considered definitive evidence of tuberculous effusion, particularly in a known case of pulmonary tuberculosis.