Results of a recent study published in the British Journal of Dermatology suggest that chronic pain experienced by patients with pachyonychia congenita (PC) may be caused by damage to the peripheral nerve fibers, with the hyperalgesia and allodynia observed in PC-affected regions likely to be manifestations of peripheral sensitization.
Investigators sought to evaluate sensory function systematically in 62 patients with PC and 45 sex- and age-matched healthy controls. All participants completed the McGill and Douleur Neuropathique-4 (DN4) questionnaires. Analyses of sensory function included the following: detection and pain thresholds, pathologic sensations, conditioned pain modulation, and temporal summation of pain.
Overall, 86% of patients with PC reported moderate to severe pain in their feet, which they described as stabbing and throbbing in quality and particularly debilitating during weight bearing/walking. Moreover, 62% of patients had DN4 scores of at least 4, implying a positive diagnosis for neuropathic pain. Although sensory testing was similar in those with DN4 scores greater than 4 compared with participants with scores less than 4, significantly higher rates of tingling (18 of 33 vs 8 of 28; P <.05) and numbness (12 of 33 vs 3 of 28; P <.05) and significantly higher chronic pain intensity (McGill Pain Questionnaire: 25.1±1 vs 17.9±1; P <.05) were reported among those with DN4 scores greater than 4 vs those with DN4 scores less than 4.
Regarding pathologic sensations, static allodynia (95% CI, 42%-67%), tingling (95% CI, 39%-68%), and electric shock-like sensations (95% CI, 32%-60%) were all highly prevalent among patients with PC. The degree of conditioned pain modulation was significantly lower among individuals with PC vs healthy controls (P <.001).
The magnitude of temporal summation of pain was similar across both arms. Patients with PC had higher thresholds for thermal sensation in both the upper and lower limbs compared with controls, as well as a significantly higher touch detection threshold in the lower limbs (P <.05), indicative of thermal and mechanical hypoesthesia. Despite higher thermal detection thresholds among those with PC, heat-pain thresholds in the feet were similar in both groups.
The investigators concluded that the clinical and physiologic features of the pain evaluated in the patients with PC in this study are suggestive of a possible neuropathic origin. In this population, the use of neuropathic pain medications may prove beneficial.
Brill S, Sprecher E, Smith FJD, et al. Chronic pain in pachyonychia congenita: evidence for neuropathic origin [published online December 6, 2017]. Br J Dermatol. doi: 10.1111/bjd.16217