Myopathy in Entrapment Neuropathy and Its Recovery after Surgical Decompression in a Rat Model

Abstract

Background: Chronic nerve compression such as carpal tunnel syndrome affect Millions of individuals due to the pain and loss of function associated with these entrapment neuropathies. Surgical decompression often helps to ameliorate some of the pathologic changes, and leads to remarkable improvement in postoperative clinical function and electro-physiologic values. However, conventional nerve conduction studies that generally used for diagnosis and follow-up only detect abnormalities in large-fiver sensory nerves and offer limited information as to the status of muscle fivers. Aim and Objectives: To study the status of myopathy in entrapment neuropathy and its recovery after surgical decompression. Materials and Methods: The right sciatic nerve of Sprague-Dawley rats was wrapped using a silastic tube of 1.3 mm inner diameter to cause chronic Nerve cobpression. Surgical decompression was performed as the removal of the tube six months later. The sciatic nerve and innervated soleus muscle of the rats were harvested at six months after entrapment and three months after surgical decompression. Toluidine blue stain for semithin section nerve specimens and histological stains with nicotine adenine dinucleotide (NADH), hematoxylin-eosin (H&E), modified Gomori trichrome and adenosine triphosphatase (ATPase) activity at pH 9.4, 4.6 and 4.3 for the muscles were perormed. Quantitative measurements of cross sectional areas (CAS) of muscle fibers were calculated and expressed as a frequency histogram. Results: The results demonstrated that after nerve entrapment there were axonal degeneration with myelin breakdown in the central region of sciatic nerve and remyelination of the axons was found after surgical decompression. The myopathy in a histopathological picture demonstrated atrophy of the muscle mingled with hypertrophy response of some muscle fibers during nerve entrapment, and showed the recovery of myopathy after surgical decompression. Conclusion: With an animal model of surgical decompression for entrapment neuropathy, this present study verified in a histopathological picture the myopathy of after long-lasting nerve entrapment, and demonstrated the recovery of muscle fivers after surgical decompression.