Lupus erythematosus cells in pleural effusion: the initial manifestation of procainamide-induced lupus erythematosus.

A 63-year-old man developed an asymptomatic pleural effusion following the administration of 500 gm of procainamide hydrochloride over a six-month period. The diagnosis was initially suggested by the finding of lupus erythematosus cells in the pleural fluid. Lupus erythematosus cells and antinuclear antibodies appeared in the blood two months later and remained for a period of six months. The diagnosis was corroborated by the presence of antibodies to denatured DNA, but not to native DNA.