Paraneoplastic motor neuron disease resembling amyotrophic lateral sclerosis in a patient with renal cell carcinoma.

OBJECTIVE To report an unusual paraneoplastic syndrome, amyotrophic lateral sclerosis, associated with renal cell carcinoma. CASE PRESENTATION AND INTERVENTION A 59-year-old man presented with muscle weakness and fasciculations in the upper extremities. Neurological examination showed that the fasciculations arose spontaneously in the upper limbs. Electrodiagnostic studies revealed an active neurogenic disorder. The patient was diagnosed with a motor neuron disease mimicking amyotrophic lateral sclerosis. Urine analysis revealed microscopic hematuria. Abdominal computerized tomography scans showed a 9.5 x 8 cm renal mass in the lower pole of the right kidney. Curative right radical nephrectomy was performed. Pathologic examination showed a clear cell adenocarcinoma. After nephrectomy, the muscle weakness and fasciculations disappeared spontaneously within 2 months. The patient was disease-free for 58 months after right radical nephrectomy. He complained of muscle weakness and fasciculation at the last follow-up again. Physical examination revealed fasciculation in the upper limbs. Abdominal tomography showed a 22 x 20 mm solid mass in the lower pole of the left kidney. Kidney-saving surgery was performed and the diagnosis of renal cell carcinoma was confirmed pathologically. Following surgery, fasciculations completely disappeared and muscle weakness diminished within 3 months. CONCLUSION This case highlights motor neuron disease as a rare paraneoplastic syndrome in association with renal cell carcinoma and resolution after removal of the tumor.