Periodic benign synovitis is characterized by the regular cyclic recurrence of articular pain, swelling, or limitation of motion without permanent deformity of the joint or injury to the bone. Forty-seven cases of this condition encountered at the Mayo Clinic were studied.

The criteria used in selecting these cases were: (1) recurrence of joint symptoms at regular intervals; (2) complete freedom from signs and symptoms between attacks; (3) absence of a specific local causative factor; and (4) absence of systemic reaction. Although the knee is the joint most frequently involved with periodic benign synovitis, any peripheral joint may be involved.

The microscopic picture of the synovial membrane obtained in cases of periodic benign synovitis is similar to that seen in cases of rheumatoid synovitis. Many who consider this microscopic picture as pathognomonic of rheumatoid arthritis may conclude that periodic benign synovitis is a rare form of rheumatoid synovitis; those who consider that this histological reaction is non-specific may favor the concept that periodic benign synovitis is a separate and distinct entity.

Spontaneous remissions are frequent, and results of medical and surgical treatment are particularly difficult to evaluate. Thus far no medical therapy has been found consistently effective. Synovectomy appears to be efficacious in cases of severely afflicted knee joints.