Background: Myasthenia gravis (MG) and neuromyelitis optica (NMO, also known as Devic disease) are rare autoimmune disorders, with upper-limit prevalence estimates in the general population of 15 per 100 000 and 5 per 100 000, respectively. To our knowledge, an association between these diseases has not been previously reported. Objectives: To describe 4 patients with MG who developed NMO after thymectomy and to analyze possible causes of apparent increased prevalence of NMO among patients with MG. Design: Case series. Patients: Four patients with MG who underwent thymectomy. Interventions: None. Results: The prevalence of MG within the published cohort of patients with NMO is more than 150 times higher than that in the general population. Conclusion: Dysregulation of B-cell autoimmunity in myasthenia, possibly exacerbated by loss of control over autoreactive cells as a result of thymectomy, may predispose patients to the development of NMO.

Between April 1982 and March 1984 7 pathologically confirmed cases of progressive multifocal leukoencephalopathy (PML) were diagnosed at our institution. Only 1 case had been seen in the preceding twenty years. Four patients had acquired immunodeficiency syndrome (AIDS). The others had chronic lymphocytic leukemia, Hodgkin's lymphoma, and systemic lupus erythematosus. All patients presented with progressive neurological deficits. In most, the initial computed tomographic (CT) scan was disproportionately less abnormal than the clinical findings. In 5 patients the first CT scan revealed hypodensities of the cerebral white matter which lacked mass effect and did not enhance with contrast agent. The lesions were observed to enlarge progressively on CT scans but often lagged behind the rate of clinical evolution. Although 3 patients were treated with cytosine arabinoside, none improved. PML had similar clinical, radiographic, and pathological features in the AIDS and non-AIDs patients. Of 79 AIDS patients cared for at our institution between December 1979 and December 1983, 3.8% had PML. PML should be suspected in AIDS patients in the presence of the characteristic CT features, especially when CT-clinical dissociation occurs.

Three patients with benign subacute osteoporotic vertebral compression fractures are presented. T1 weighted magnetic resonance (MR) images (SE 500/30) showed decreased vertebral signal. Because the results of the MR examination were thought to indicate malignant disease, extensive medical workups, including one biopsy, were pursued in all three patients. Routine (SE 500/30) spin-echo pulse sequences cannot definitively distinguish between benign and malignant vertebral compression fractures.

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