Adult-onset Still's disease. Twenty-year followup and further studies of patients with active disease.

Eleven female patients with adult-onset Still's disease were followed for 7-36 years (mean 20.2 years) after the onset of their illness. Ten of these patients had a chronic course characterized by remissions and exacerbations of arthritis associated with fever and rash. Five patients had terminal interphalangeal involvement, and carpal ankylosis was demonstrated on x-ray film in 10. Two patients developed a widespread polyarthritis, and renal amyloidosis was diagnosed 10 years after disease onset in the most severely affected patient. In 4 patients studied during an exacerbation of the disease, circulating immune complexes were detected by the staphylococcal A binding assay, but not by the C1q binding assay. Synovial fluid analysis in 1 patient revealed a low C3 level and total hemolytic complement (CH50) together with immune complexes and IgG rheumatoid factor. Immune complexes were not identified in the characteristic Still's rash by immunofluorescence or electron microscopy, although mast cell degranulation, neutrophil lysis, and perivascular fibrin deposition were reminiscent of immune complex--mediated vascular injury. The clinical and laboratory features as well as the long-term course of adult- and juvenile-onset systemic Still's disease are similar, but further studies of genetic markers and immunopathology are required to establish a common pathophysiology.