Introduction

Pigmented villonodular synovitis is a rare disease of unknown etiology mostly affecting the knee and foot. Until now an association with autoimmune diseases has not been reported.

Case presentation

The diagnosis of systemic lupus erythematosus was made in a 15-year-old Caucasian girl based on otherwise unexplained fatigue, arthralgia, tenosynovitis, leukopenia, low platelets and the presence of antinuclear and deoxyribonucleic antibodies. At the age of 20 a renal biopsy revealed lupus nephritis class IV and she went into complete remission with mycophenolate mofetil and steroids. She was kept on mycophenolate mofetil for maintenance therapy. At the age of 24 she experienced a flare-up of lupus nephritis with nephrotic syndrome and new onset of pain in her right hip. Magnetic resonance imaging, arthroscopy and subtotal synovectomy identified pigmented villonodular synovitis as the underlying diagnosis. Although her systemic lupus erythematosus went into remission with another course of steroids and higher doses of mycophenolate mofetil, the pigmented villonodular synovitis persisted and she had to undergo open synovectomy to control her symptoms.

Conclusion

Systemic lupus erythematosus is associated with many different musculoskeletal manifestations including synovitis and arthritis. Pigmented villonodular synovitis has not previously been reported in association with systemic lupus erythematosus, but as its etiology is still unknown, the present case raises the question about a causal relationship between systemic lupus erythematosus and pigmented villonodular synovitis.