An unusual case of systemic lupus erythematosus, lupus nephritis, and transient monoclonal gammopathy.

A 23-year-old female patient suffering from active systemic lupus erythematosus (SLE) was treated with azathioprine (2 mg/kg per day) and prednisone. Lupus nephritis class III with increasing proteinuria developed 28 months after disease onset. Treatment was switched to monthly pulse cyclophosphamide administered intravenously for 6 months (total dose 6.3 g), followed by oral azathioprine and low-dose prednisone to maintain partial remission. Eight months later, the patient developed an acute exacerbation of SLE with fever, proteinuria of 9.1 g/day, pancytopenia, and cerebral involvement with cephalgias and a grand mal seizure. She responded well to high-dose corticosteroids (500 mg prednisolone pulses over 3 days, i.v.) and was azathioprine switched from to methotrexate (12.5-15 mg per week). Under this treatment, lupus activity gradually decreased and the patient felt well again. Five years after the initial diagnosis of SLE, a rapidly increasing immunoglobulin G-kappa type (IgG-kappa) monoclonal gammopathy developed, reaching a maximal serum paraprotein concentration of 73.5 g/l. Bone marrow biopsy revealed 15% of moderately abnormal, highly differentiated plasma cells arranged in small clusters and expressing IgG-kappa. No bony lesions were detectable on skeletal radiographs. Pulses of dexamethasone (40 mg) were administered and led to a transient decrease of paraproteinemia to a minimum of 31.9 g/l, followed by an increase to 62 g/l. At that point, high-dose chemotherapy supported by autologous stem cell transplantation was considered. Due to an intermittent pneumococcal septicemia, methotrexate was discontinued and dexamethasone was replaced by 5-10 mg cloprednol. At this point, totally unexpectedly, the paraprotein decreased spontaneously without any further cytostatic treatment and was no longer detectable 1 year later. Concomitantly, plasma cell counts in bone marrow biopsies fell to below 5%. As SLE remained inactive, the patient became pregnant and gave birth to a healthy child. During late pregnancy, SLE activity flared up with rising proteinuria and blood pressure. Therefore, after delivery, cyclophosphamide (100 mg/day, orally) was readministered for 4 months, resulting in an improvement of kidney function with stable proteinuria of 1-2 g/l to date. Paraproteins are no longer detectable. In conclusion, this case report documents the rare event of transient paraproteinemia in a patient with SLE. A self-limiting regulatory defect in the control of a terminally differentiated B-cell clone may be the origin of this phenomenon.