Diabetes mellitus is recognised as a risk factor for carpal tunnel syndrome. The response to treatment is unclear, and may be poorer than in non-diabetic patients. Previous randomised studies of interventions for carpal tunnel syndrome have specifically excluded diabetic patients. The aim of this study was to investigate the epidemiology of carpal tunnel syndrome in diabetic patients, and compare the outcome of carpal tunnel decompression with non-diabetic patients. The primary endpoint was improvement in the QuickDASH score. The prevalence of diabetes mellitus was 11.3% (176 of 1564). Diabetic patients were more likely to have severe neurophysiological findings at presentation. Patients with diabetes had poorer QuickDASH scores at one year post-operatively (p = 0.028), although the mean difference was lower than the minimal clinically important difference for this score. After controlling for underlying differences in age and gender, there was no difference between groups in the magnitude of improvement after decompression (p = 0.481). Patients with diabetes mellitus can therefore be expected to enjoy a similar improvement in function.

Impingement syndrome in the shoulder has generally been considered to be a clinical condition of mechanical origin. However, anomalies exist between the pathology in the subacromial space and the degree of pain experienced. These may be explained by variations in the processing of nociceptive inputs between different patients. We investigated the evidence for augmented pain transmission (central sensitisation) in patients with impingement, and the relationship between pre-operative central sensitisation and the outcomes following arthroscopic subacromial decompression.

We recruited 17 patients with unilateral impingement of the shoulder and 17 age- and gender-matched controls, all of whom underwent quantitative sensory testing to detect thresholds for mechanical stimuli, distinctions between sharp and blunt punctate stimuli, and heat pain. Additionally Oxford shoulder scores to assess pain and function, and PainDETECT questionnaires to identify ‘neuropathic’ and referred symptoms were completed. Patients completed these questionnaires pre-operatively and three months post-operatively.

A significant proportion of patients awaiting subacromial decompression had referred pain radiating down the arm and had significant hyperalgesia to punctate stimulus of the skin compared with controls (unpaired t-test, p < 0.0001). These are felt to represent peripheral manifestations of augmented central pain processing (central sensitisation).

The presence of either hyperalgesia or referred pain pre-operatively resulted in a significantly worse outcome from decompression three months after surgery (unpaired t-test, p = 0.04 and p = 0.005, respectively).

These observations confirm the presence of central sensitisation in a proportion of patients with shoulder pain associated with impingement. Also, if patients had relatively high levels of central sensitisation pre-operatively, as indicated by higher levels of punctate hyperalgesia and/or referred pain, the outcome three months after subacromial decompression was significantly worse.