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Although corticosteroids alleviate weakness in mdx mice, no long-term treatment has determined whether this benefit is maintained. We studied mdx mice forelimb grip strength and fatigue from 3 through 84 weeks and followed survival through 104 weeks. The mdx mice were given twice weekly oral prednisolone (5 mg/kg) beginning at 3 or 4 weeks. Treated mdx mice survived longer than untreated mice. Between 3 and 10 weeks, treated and untreated mdx mice had similar strength. Between 10 and 24 weeks, strength and strength per gram body weight declined more slowly in treated than untreated mdx mice. Between 24 and 84 weeks, treated and untreated mdx mice declined in strength at the same rate, although treated mice remained stronger. Forelimb grip fatigue was present in untreated mdx mice at all time-points compared to wild-type and was not changed significantly by treatment. We have demonstrated long-term benefit of oral prednisolone in the mdx mouse model of Duchenne muscular dystrophy (DMD). As corticosteroids remain the most validated long-term treatment of DMD, this work may allow for better prediction of synergistic treatments likely to translate to effective improvement for boys with this progressive muscular dystrophy. A number of mouse model systems for the study of Duchenne muscular dystrophy (DMD) exist. The most highly characterized is the dystrophin-deficient mdx strain on the C57BL10J background carrying a mutation in exon 23 of the X-linked dystrophin gene. Our previous work established a reproducible methodology for the study of strength and fatigue in the mdx mouse, the dystrophin/utrophin-deficient mouse (mdx; utrn Ϫ/Ϫ ), and the ␣2-laminin mutation (dy/dy), all on the C57BL6 background. 8 We demonstrated efficacy of weekly oral steroids in the dydy model of congenital muscular dystrophy. 9 Although there is some debate about how well the mdx mouse models DMD, few long-term in vivo studies of strength have been performed. 6,8 Here we studied the well-established mdx C57BL/10J mouse model, emphasizing long-term strength and mortality evaluation. We measured prednisolone-treated and untreated mdx mice over 2 years. We demonstrate improved survival and strength in this model with oral, twice-weekly prednisolone treatment. Given that corticosteroids are currently the best treatment for boys with DMD and that multiple pharmacologic agents may be necessary to improve outcome, it is critical to demonstrate in an animal model which drugs are acting by the same pathway or by synergistic or antagonistic pathways for sustained periods of time. METHODSMice. Pathogen-free mdx C57BL10J ScSn , wild-type C57BL10J ScSn , and C57BL10J breeding mice were used (Jackson Laboratories, Bar Harbor, Maine). All mice were maintained in micro-isolator cages in accordance with guidelines of our institutional Committee for the Humane Care of Laboratory Animals and the NIH.Strength and Fatigue Measurement. Male mice were weighed and examined for forelimb strength at the time of weaning (3 or 4 weeks); at 6, 8, 10, and 12Ab...

Our data show that 60% of patients with muscle cramps who lack neuropathic complaints have SFN, as documented by decreased IENFD. Cramps may originate as local mediators of inflammation released by damaged small nerve that excite intramuscular nerves.

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