Carpal Tunnel Syndrome and Diabetes. Surgical outcome and nerve pathology

Abstract: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in the upper extremity. Diabetes mellitus increases the risk of developing CTS from an estimated prevalence of 2-4% in the general population to 15-30% in diabetics. Results after carpal tunnel release in diabetic patients with CTS have been sparsely investigated and the basis for its increased prevalence in diabetes is yet unknown. In a prospective study, 35 consecutive patients with diabetes and CTS were age and gender matched with 31 non-diabetic patients with CTS. Operations were performed by the same surgeon and follow-up investigations were completed independently by the same occupational therapist. Pre-operatively, 6, 12 and 52 week’s post-surgery, clinical outcomes and health-related quality of life (HRQL) were registered. Nerve conduction studies were performed, preoperatively, and after 52 weeks. At time of surgical carpal tunnel release, punch skin biopsies as well as a posterior interosseous nerve (PIN) biopsy were performed at wrist level. The utility of the PIN biopsy method was investigated in 10 Type 2 diabetic subjects, recruited from a population-based health screening programme. Clinical investigations revealed that diabetic patients with CTS, achieve the same beneficial outcome after carpal tunnel release as non-diabetic patients. Only cold intolerance was relieved to a lesser extent for diabetic patients. HRQL was impaired in diabetic patients with CTS and population norms were not achieved after carpal tunnel release. However, disease-specific symptomatic and functional improvements after surgery did not differ between diabetic and non-diabetic patients. Nerve conduction parameters were noticeably impaired in diabetic patients but did not preclude significant recovery after carpal tunnel release. The skin biopsies did not demonstrate a difference in intraepidermal nerve fibre density (IENFD) between diabetic and non-diabetic patients. However, it did indicate higher IENFD in females than in males, and in hairy compared to glabrous skin. The PIN biopsy procedure fulfils the criteria of a nerve biopsy and was well tolerated by the patients. It demonstrated reduced myelinated nerve fibre and endoneurial capillary densities in the forearm of both diabetic and non-diabetic patients. Reduced myelinated nerve fibre density was further accentuated in diabetic patients. This thesis concludes that diabetic patients with CTS should be offered the same opportunities for carpal tunnel release as non-diabetic patients, despite notably impaired nerve conduction parameters. Nerve pathology may predispose patients to CTS which is further accentuated in diabetes.