Overflow proteinuria as a manifestation of unrecognized polymyositis
A 41-year-old man visited our clinic with swelling and weakness of both lower extremities of 1-month duration. Recently, he had begun to have pain in both thighs and difficulty in lifting his legs. He had no history of recent trauma, administration of drugs, infections, physical exercise, endocrinopathies, or other factors that could cause rhabdomyolysis. On physical examination, there was pitting edema of the lower extremities without cutaneous eruption. shows the laboratory data. He recently noticed that his urine was tea-colored. The urine dipstick showed a positive test for blood in the absence of red cells in the sediment. The spot urine protein-to-creatinine ratio was 1,714 mg/g. His serum myoglobin was 0.405 mg/dL and urine myoglobin was undetectable. Aggressive volume replacement was started for the treatment of rhabdomyolysis.\nA 24-hour urine collection showed protein excretion of 3,140 mg/day and albumin excretion of 122.5 mg/day. Albuminuria was 3.9% of total proteinuria. The electrophoretic analysis of the serum and urine proteins is shown in . The serum electrophoresis pattern showed decreased albumin and increased α1-fraction, β-fraction, and γ-globulins, suggesting polyclonal gammopathy (). The urine electrophoresis showed increased β-fraction, which accounted for 53.3% of the urinary proteins (). Immunofixation of serum and urine was performed to identify monoclonal immunoglobulins and/or free light chains, and gave negative results. Despite fluid replacement, the patient’s creatine phosphokinase (CPK) level increased to 21,450 IU/L and his leg weakness did not improve. Nerve conduction studies were normal but the electromyography showed short-duration, low-amplitude, and polyphasic patterns in all of the left upper and lower extremity muscles, suggesting inflammatory myopathy. The test for anti-Jo-1 antibody was positive, with a titer more than 8.0 EU. Biopsy of the left vastus lateralis muscle demonstrated endomysial chronic inflammation and muscle fiber necrosis (), and immunohistochemical stain showed infiltration by CD8+ T cells (). Polymyositis was diagnosed by the criteria of Bohan and Peter, as he had symmetric proximal muscle weakness, histologic evidence of myositis, elevated serum muscle enzymes, and characteristic myopathic changes on electromyography, without skin changes. The patient was started on prednisone, 1 mg/kg daily, which resulted in gradual improvement of his leg pain, weakness, and swelling. After 1 month, his CPK level decreased to 461 IU/L and the spot urine protein-to-creatinine ratio decreased to 24.1 mg/g.