Regional migratory osteoporosis is an uncommon entity characterized by sudden attacks of migrating lower extremity paraarticular pain, local edema, and muscle atrophy; the disease is verified by radiologic demineralization and bone scan uptake. The etiology and pathogenesis are unknown. We describe a case of regional migratory osteoporosis followed over nine years by serial electromyographic studies documenting denervation patterns coincident in time and location of each acute attack. The substantiation of denervation in regional migratory osteoporosis is of both diagnostic and pathogenetic significance. clinical picture emerged of severe lower extremity paraarticular pain, muscle atrophy, and localized edema associated with radiologic osteoporosis, with the symptoms lasting 4 t o 12 months (2-13). T h e diagnosis was usually made by exclusion. Multiple biopsies were needed to exclude infectious, granulomatous, and neoplastic diseases.A patient with multiple attacks who was followed over a 9 year period is described. Electromyogram ( E M G ) abnormalities of denervation coincided both anatomically and chronologically to the clinically involved areas. CASE REPORTA SS-year-old white female presented to Harbor General Hospital in June 1966 after 6 months of unprovoked left knee pain followed by 3 months of pain and swelling of the left foot and ankle. She was taking no medication. Physical examination revealed weakness and muscle atrophy confined to the left thigh and calf with grade 4/5 muscle strength in the left quadriceps and anterior tibia1 muscles (strength judged on a 0 to 5 scale with 5/5 normal, 4/5 and 3/5 moderate, 2/5 minimal resistance against gravity, and 1/5 flicker movements). A livido skin pattern overlaid brawny edema of the left foot and ankle. Motion was limited by tenderness and pain. Neurologic examination was normal.Laboratory values that were normal included urinalysis, CBC, calcium, phosphorus, alkaline phosphatase, BUN, creatinine, uric acid, and 24 hour urine calcium. The Wintrobe ESR was 40-50 mm/hr, cholesterol value was 283 mg/dl, and a first strength PPD was positive. Serum electrophoresis, immunoglobulin levels, cryoglobulin, urinary Bence Jones protein, latex fixation, and anti-nuclear antibody studies were also