Syringomyelia presenting as shoulder instability.

Three middle-aged women presented with shoulder instability as the first sign of syringomyelia. The patients' symptoms were unilateral in each case. Two patients had posterior shoulder instability, and one patient had anterior instability. Two patients had undergone surgery to stabilize the shoulder before referral to our center. In both cases the surgery had been unsuccessful. Review of two of the patients' plain radiographs after referral demonstrated radiographic changes highly suggestive of neuropathic arthropathy. The diagnosis of syringomyelia was confirmed by myelography, computed tomographic scanning, and magnetic resonance imaging. One patient had an associated Arnold-Chiari malformation that was treated by a syringosubarachnoid shunt. Each patient's shoulder disability, although significant, remained static throughout a follow-up period averaging 79 months. Shoulder instability can be a presenting symptom and sign of syringomyelia. Patients over age 40 presenting with a glenohumeral dislocation may, in addition to having a high probability of rotator cuff injury, have neuropathic arthropathy. Syringomyelia should be included in the differential diagnosis of shoulder instability so that unnecessary and unsuccessful surgery can be avoided.