Introduction: Carpal tunnel syndrome is a prevalent condition, affecting approximately 1-5% of the general population. The prevalence of median nerve schwannomas among patients diagnosed with carpal tunnel syndrome is largely unknown and limited to case reports. The pathophysiology and natural history of schwannomas in patients with carpal tunnel syndrome is also unclear.

Methods: Retrospective single-institution chart review from July 2014 to February 2015 of the incidence of median nerve schwannomas in patients diagnosed with carpal tunnel syndrome undergoing surgery for carpal tunnel release.

Results: Median nerve schwannomas were found intra-operatively in 2/50 (4%) patients. Patient 1 was a 51 year-old male, and patient 2 was a 53 year-old female. Pre-operative cervical spine MRI of patient 1 demonstrated C5-6 and C-7 spondylosis and right-sided foraminal stenosis, and EMG showed acute right C6 radiculopathy, acute-on-chronic right C7 radiculopathy, and severe median neuropathy in the wrists bilaterally. Cervical spine MRI of patient 2 showed bilateral C6 radiculopathy, and EMG demonstrated additional moderate median neuropathy in the wrists, bilaterally, worse on the right. Both patients maintained full motor strength on pre-operative assessment. Intra-operatively, small benign-appearing tumors (2 tumors in patient 1; 1 tumor in patient 2) originating from the median nerve fascicles were noted, suggestive of schwannomas. To avoid risk of post-operative motor impairment, tumor resection was deferred in both cases in favor of decompression alone. At two-week follow-up, both patients voiced significant improvement in pain symptoms and maintained full motor function.

Conclusions: Our findings suggest the prevalence of median nerve schwannomas among patients with carpal tunnel syndrome may be greater than previously thought. Carpal tunnel release alone effectively provides symptomatic relief, but serial MRIs of the affected wrist are recommended to monitor tumor growth. Future prospective studies are required to investigate the natural history of median nerve schwannomas in patients with carpal tunnel syndrome and to determine the role of resection versus observation of these lesions. Additionally future basic science studies are warranted in order to investigate the pathophysiology of such lesions which may involve reactive processes in the nerve secondary to repetitive trauma with the hyperthrophic transverse carpal ligament.

Patient Care: This series emphasizes that the incidence of median nerve schwannomas in patients with carpal tunnel syndrome may be underestimated in the literature, ultimately leading to an increasing awareness of such possible diagnosis among neurosurgeons as well as emphasizing the necessity of future clinical and basic science studies on the natural history and pathophysiology of such disease.

Learning Objectives: 1. To understand that that incidence and natural history of median nerve schwannomas in the patients presenting with symptoms of carpal tunnel syndrome are largely unknown in the literature. 2. To acknowledge that future research is necessary in order to provide a better understanding on the pathophysiology and natural history of median nerve schwannomas in patients with carpal tunnel syndrome. 3. To recognize that, while carpal tunnel release effectively alleviates patient symptoms, the role of resection versus observation in the management of median nerve schwannomas is unknown and warrants further investigation.

References: [1] Atroshi I, Gummesson C, Johnsson R, Ornstein E, Ranstam J and Rosen I. Prevalence of carpal tunnel syndrome in a general population. JAMA 1999; 282: 153-158. [2] Aslam N and Kerr G. Multiple schwannomas of the median nerve: a case report and literature review. Hand Surg 2003; 8: 249-252.