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

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 i.v. 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 i.v. immunoglobulin has significantly increased compared to plasma exchange and thymectomy.

Effects of ramped amplitude waveforms on the onset response of high-frequency mammalian nerve block.

Though high-frequency alternating current (HFAC) can block nerve conduction, the block is invariably preceded by an onset response which is a period of repetitive nerve firing. We tested the hypothesis that slowly ramping up the amplitude of the HFAC waveform could produce block without this initial onset response. Computer simulations were performed, using the McIntyre-Richardson-Grill (MRG) model of myelinated mammalian axon. A ramped-amplitude HFAC was applied to axons of diameters ranging from 7.3 microm to 16 microm and at frequencies ranging from 3125 Hz to 40 kHz. The ramped-amplitude HFAC was also investigated in vivo in preparations of rat sciatic nerve. Sinusoidal voltage-regulated waveforms, at frequencies between 10 kHz and 30 kHz, were applied with initial amplitudes of 0 V, linearly increasing with time to 10 V. Ramp durations ranged from 0 s to 60 s. In both the MRG model simulations and the experiments, ramping the HFAC waveform did not eliminate the onset response. In the rat experiments, the peak amplitude of the onset response was lessened by ramping the amplitude, but both the onset response duration and the amount of onset activity as measured by the force-time integral were increased.

A modified technique for insertion of a unit rod into the pelvis.

The use of a pedicle probe facilitated insertion of a unit rod into the ilium of five patients with neuromuscular scoliosis. Compared to the standard technique, the pedicle probe method greatly reduced soft-tissue dissection and also provided better perception of rod alignment and cortical perforation.