Muscular Disorders in Osteomalacia

Osteomalacia results from vitamin D deficiency. The pathophysiology of the myopathy is unknown.

Symptoms and Signs

About one third of osteomalacia patients have muscle weakness; of these patients, almost all initially report weakness in the pelvic and thigh muscles. Typically, the patient has pain in the back, hip girdle, and legs. Muscle wasting is proportionate to weakness. About half of patients have a waddling gait and use Gowers' maneuver to rise from the supine position (rolling to prone position, kneeling, then rising to standing by pushing with hands against shins, knees, and thighs). About 20% of patients have a marked limp or cannot walk. Tendon reflexes are normal to brisk, and sensation is normal. No cranial nerve abnormalities occur. Bone pain and tenderness are most prominent in the pelvis, femurs, spine, and ribs. Frequently, the vertebrae collapse, sometimes causing skeletal deformities. Occasionally, patients describe total body pain, suggesting a primary psychiatric disorder.

Diagnosis

The serum CK level is normal or slightly elevated. Electromyography may show a myopathic pattern; the results of nerve conduction studies are normal. Muscle biopsy findings are normal or indicate nonspecific changes.

Prognosis and Treatment

For most patients, the long-term prognosis is good. However, if muscle wasting, especially of the quadriceps muscle of the thigh, is marked, patients may never regain full strength despite restoration of normal serum levels of vitamin D and phosphate.