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January 2009

Motor Nerve Hyperexcitability and Muscle Cramps in Machado-Joseph Disease—Reply

Arch Neurol. 2009;66(1):138-141. doi:10.1001/archneurol.2008.514

In reply

We are very pleased with the comments raised by Kanai and Kuwabara regarding our study. Our findings in the series of Brazilian patients with MJD indeed confirm previous results reported by Kanai et al,1 indicating that muscle cramps are a frequent and disabling manifestation of the disease.

We failed to identify significant clinical and neurophysiological differences between patients with and without cramps in our study. However, cramps were mostly found in patients of clinical subtype 1. In addition, H-reflex and F-wave studies suggested increased excitability of the motor neuron pool in patients with cramps. These results led us to consider the possibility that pyramidal dysfunction might cause abnormal modulation of motor neuron excitability and thus might play an important role in the origin of cramps. However, it is important to point out that our hypothesis and the hypothesis raised previously by Kanai et al1 regarding the intrinsic peripheral damage are not mutually exclusive. They may indeed work together in determining the pathophysiology of muscle cramps, and the relative contribution of each one may vary for each patient. Cramps may be found in different neurological and nonneurological conditions. Although neuromuscular diseases certainly rank among the first, central nervous system disorders such as stiff-person syndrome and multiple sclerosis are frequently accompanied by cramps. The pathophysiology of cramps thus reflects this heterogeneity; therefore, it is unlikely that all types of cramps share the same exact mechanisms.

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