Can skin disease cause neuropathic pain? A study in pachyonychia congenita.

Introduction: Pachyonychia congenita (PC) is a rare skin disorder caused by an autosomal dominant mutation in one of five genes encoding keratin (K6a, K6b, K6c, K16 or K17; each defining one PC subtype). Pain is a prominent symptom, but its severity and type are poorly characterized.

Methods: In total, 35 genotyped US patients with PC consented to clinical assessment including the quality of life (QoL) questionnaire EQ-5D-3L, the Brief Pain Inventory (BPI) and painDETECT. Abbreviated quantitative sensory testing (QST) was also performed, and included mechanical detection threshold (MDT), mechanical pain threshold (MPT), wind-up pain ratio (WUR) and vibration detection threshold (VDT).

Results: Significant pain in patients with PC was confirmed, as indicated by mean BPI severity and interference of 4.2 ± 1.7 and 4.4 ± 2.2, respectively, as well as QoL impairment, as indicated by mean EQ-5D index of 0.69 ± 0.18. PD identified neuropathic pain in 62% of patients, the remainder being nociceptive. The painDETECT score was most significantly related to EQ-5D index (R(2)  = 0.26, P = 0.02). The K17 and K6a subtypes exhibited significantly worse QoL (0.584 and 0.613 respectively) than the K16 and K6b subtypes (P = 0.02). In QST analysis, abnormal pressure pain (assessed as MPT) was frequently observed, with more than half of patients with PC affected (54%), and 57% of patients with K17 also exhibiting abnormality in minimum touch threshold (assessed as MDT, P < 0.05). Very few patients were receiving analgesic therapy appropriate for neuropathic pain.

Conclusion: Significant neuropathic pain was observed in PC, which warrants appropriate treatment. The health states observed in this sample are at a level that the average US citizen would forfeit one-third of their remaining lifespan to avoid.