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Incidence and mortality rates of myasthenia gravis and myasthenic crisis in US hospitals

From The Neurological Institute (A.A., J.D.M., B.K., D.C.P.), University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, OH; and the Department of Neurology & Psychiatry (H.J.K.), Saint Louis University, St. Louis, MO.

Address correspondence and reprint requests to Dr. Amer Alshekhlee, Department of Neurology, University Hospitals Case Medical Center, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106-5040 amer.alshekhlee{at}uhhospitals.org

Objective: To determine the incidence and mortality rates and predictors of death in myasthenia gravis (MG) and MG crisis in a large US cohort.

Methods: Our cohort was identified from the Nationwide Inpatient Sample database for the years 2000 through 2005 using ICD-9-CM codes. MG crisis was identified by the principal diagnosis code or by the presence of respiratory failure. The incidence of MG was stratified by age, ethnicity, and gender. Multivariate logistic regression analysis was used to identify predictors of mortality in MG. For trend analyses of immune intervention, we used the Cochrane-Armitage test.

Results: After data cleansing, 5,502 patients with MG were included. In women, the incidence of admission was two to three times higher during the first 5 decades. In men, the incidence of admission was higher during the sixth, seventh, and eighth decades. The annual incidence rate of MG was higher in black women (0.01 per 1,000 persons/year) compared to white women and white and black men (0.009, 0.008, and 0.007 per 1,000 persons/year). The overall in-hospital mortality rate was 2.2%, being higher in MG crisis (4.47%). Older age and respiratory failure were the predictors of death, with adjusted odds ratios of 9.28 (95% confidence interval [CI], 3.31, 26.0) and 3.58 (95% CI, 2.01, 6.38). The trend of IV immunoglobulin utilization has increased compared to plasma exchange and thymectomy (p < 0.0001).

Conclusion: Myasthenia gravis (MG) is still a disease of young women and old men, as reflected by the hospital admission rates. In-hospital mortality of MG is low. Hospital utilization of IV immunoglobulin has significantly increased compared to plasma exchange and thymectomy.

Abbreviations: BiPAP = bilevel positive airway pressure; CI = confidence interval; CPAP = continuous positive airway pressure; ICD-9-CM = International Classification of Diseases, 9th edition–Clinical Modification; ICF = intermediate care facility; IVIg = IV immunoglobulin; MG = myasthenia gravis; NIS = Nationwide Inpatients Sample; OR = odds ratio; PE = plasma exchange; SNF = skilled nursing facility.

Supplemental data at www.neurology.org

Disclosure: The authors report no disclosures.

Received September 13, 2008. Accepted in final form February 9, 2009.