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46-year-old woman presents with sensory loss and paresthesia in her upper extremities and across her upper chest, with weakness in her intrinsic handmuscles bilaterally. The symptoms began about 2 years ago, initially involving a much narrower region, but the symptoms have gradually spread. She wasinvolved in a severe car accident 3 years ago and has had neck pain ever since,but she sustained no fractures or head injury. Her examination is notable forweakness and atrophy of the intrinsic hand muscles, brisk lower extremityreflexes, and loss of pain and temperature sensation in the C5 through T2dermatomes bilaterally, with normal sensation above and below those levels.MRI scan shows syringomyelia centered at C8 but extending up to C4 and downto T2. Which of the following patterns of upper extremity nerve conduction study results would be most typical in this scenario?
Explanation
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In syringomyelia, the sensory deficits are due to damage to the decussating spinothalamic tract fibers in the anterior spinal cord. While needle EMG typically shows a characteristic pattern of upper extremity denervation (most commonly at C8-T1) and CMAP amplitudes recording from affected hand muscles are reduced, sensory nerve conduction studies remain normal because the damage does not disrupt the connection between the sensory neurons peripheral terminals and their cell bodies in the dorsal root ganglion.
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Reference
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Page 61,Tavee JO, Levin KH. Myelopathy due to degenerative and structural spine diseases. Continuum (Minneap Minn). 2015 Feb21(1 Spinal Cord Disorders)52-66. doi 10.121201.CON.0000461084.71618.35. PMID 25651217.
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Option 1
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Is Correct (Option 1):
Abnormal compound muscle action potentials (CMAPs), abnormal sensory nerve action potentials (SNAPs)
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Option 2
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Is Correct (Option 2):
Abnormal CMAPs, normal SNAPs
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Option 3
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Is Correct (Option 3):
Normal CMAPs, abnormal SNAPs
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Option 4
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Is Correct (Option 4):
Normal CMAPs, normal SNAPs
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