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Chapter 5. Neuromuscular Diseases

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A 45-year-old man presents with a right foot drop and numbness across the lateral part of the leg and the dorsum of the right foot. He intentionally lost 20 pounds recently and admits to frequently crossing his legs when watching television. His right foot drop improved over the course of few months; however, he developed weakness in his left hand. Nerve conduction studies/electromyogram (NCS/EMG) revealed an ulnar neuropathy with conduction block across the elbow. His father and sister did have similar episodes in the past.

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What would be the best next step in management?

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(A) Spinal tap

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(B) Magnetic resonance imaging (MRI) of the lumbar and cervical spine

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(C) Genetic testing

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(D) Start IV steroids

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(E) Nerve biopsy

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(C) Hereditary neuropathy with liability to pressure palsy (HNPP) is inherited in an autosomal- dominant pattern. HNPP is caused by a deletion on chromosome 17p11.2, in the PMP-22 gene. Patients usually describe painless numbness and weakness in the distribution of a single peripheral nerve. Symptomatic mononeuropathies are often precipitated by trivial compression of nerves, such as crossing legs or leaning on the elbows. Symptoms usually recede over several weeks to months. The most affected nerves are the median nerve at the wrist, ulnar nerve at the elbow, and peroneal nerve at the fibular head. NCS usually demonstrate demyelinating findings across compression sites. Nerve biopsies typically demonstrate globular thickening of the myelin sheath, which resembles sausage, or tomacula.

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The best next step in management, in a patient who has a typical history and physical examination findings of multiple mononeuropathies with a strong family history after obtaining NCS/EMG and demonstrating demyelinating features across compression sites, would be to do genetic testing to detect the deletion on chromosome 17p11.2 in the PMP gene. Typically, MRI of the cervical and lumbar spine and CFS analysis should be normal. IV steroids are not helpful. While a nerve biopsy can reveal tomacula and reduction in the large myelinated fibers, it is still considered an invasive procedure, and genetic testing is a more definitive diagnosis. (Amato, 167–169; Potulska-Chromik, 914–918)

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Amato AA, Russell JA. Neuromuscular Disorders. New York, NY: McGraw-Hill; 2008.

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Potulska-Chromik A, Sinkiewicz-Darol E, Ryniewicz B, et al. Clinical, electrophysiological, and molecular findings in early onset hereditary neuropathy with liability to pressure palsy. Muscle Nerve. 2014;50:914–918.

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A 10-year-old boy is accompanied by his mother to the neuromuscular clinic with complaints of bilateral foot drop and wasting of the foot and leg muscles. The mother stated that her son has always been clumsy and has had trouble in gym class. He ...

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