Chronic pain in Pachyonychia Congenita: evidence for neuropathic origin

Abstract

Background

Pachyonychia congenita (PC) is a rare autosomal dominant skin disease with chronic pain being the most prominent complaint. Histological studies showing alterations in sensory innervation along with few reports on alterations in mechanical sensitivity suggest that PC may be a form of neuropathy.

Objective

To systematically evaluate sensory function of PC patients vs. controls, here for the first time, in order to investigate PC pathophysiology.

Methods

Patients (n=62) and controls (n=45) completed the McGill and Douleur Neuropathique-4 (DN4) questionnaires. Sensory testing included: detection and pain thresholds, pathological sensations, conditioned pain modulation (CPM) and temporal summation of pain (TSP).

Results

A moderate-severe chronic pain in the feet, throbbing and stabbing in quality, was highly prevalent among PC patients (86%) and especially debilitating during weight bearing. In addition, the majority of patients had DN4 score ≥4 (62%), static allodynia (55%) and tingling (53%) in the feet. Compared to controls, PC patients exhibited thermal and mechanical hypoesthesia and mechanical hyperalgesia in the feet. CPM was reduced among the patients, and associated with more enhanced feet mechanical hyperalgesia. The specific gene and nature of the causative mutation did not affect any of these features.

Conclusion

Although thermal and mechanical hypoesthesia may result from thicker skin, its presentation in painful regions along with mechanical hyperalgesia and allodynia point towards the possibility of neuropathic changes in PC. The clinical features and DN4 scores support this possibility and therefore neuropathic pain medications may be beneficial for PC patients.

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