Extra-median spread of sensory symptoms in carpal tunnel syndrome suggests the presence of pain-related mechanisms

Patients with carpal tunnel syndrome (CTS) may complain of sensory symptoms outside the typical median nerve distribution. The study is aimed to understand which clinical features are associated with the extra-median distribution of symptoms in CTS. We recruited 241 consecutive CTS patients. After selection, 103 patients (165 hands) were included. The symptoms distribution was evaluated with a self-administered hand symptoms diagram. Patients underwent objective evaluation, neurographic study and a self-administered questionnaire on subjective complaints. No clinical or electrodiagnostic signs of ulnar nerve involvement were found in the 165 hands. Median distribution of symptoms was found in 60.6% of hands, glove distribution in 35.2% and ulnar distribution in 4.2%. Objective measures of median nerve lesion (tactile hypaesthesia and thenar muscles hypasthenia) and neurographic involvement were significantly more severe in median hands than in the other groups. Subjective complaints (nocturnal pain, numbness and tingling sensations) were significantly more severe in glove hands. Neurophysiological and objective measures were not correlated with subjective complaints. The severity of the objective examination and neurographic involvement and the intensity of sensory complaints appear to be independent factors that influence the symptoms distribution. Extra-median spread of sensory symptoms was associated with higher levels of pain and paresthesia. We suggest that central nervous system mechanisms of plasticity may underlie the spread of symptoms in CTS.