Rare Skin Disorder Brings Extraordinary Pain

Pachyonychia congenita (PC), a rare skin disorder, can cause an inordinate amount of neuropathic pain, a study in Clinical and Experimental Dermatology confirms. In the chilling words used by the researchers, “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.”

PC is a very rare autosomal dominant skin disorder characterized predominantly by nail dystrophy and painful palmoplantar keratoderma. The rarity of the condition has limited the clinical research devoted to it. Large population-based studies are not possible, and much of the published information on the condition has been based on single case studies. Despite its rarity, however, PC is one of those conditions for which the genetic mutations are well-known: it is caused by a mutation in one of five keratin genes including K6a, K6b, K6c, K16, or K17, which produce the tough proteins that support skin cells and give them shape and strength in healthy individuals.

It is well-known from earlier research that PC — which isn’t life threatening on its own – brings constant pain. Pain from PC generally comes from the formation of cysts, painful calluses, and the blisters that regularly form under those calluses. But the current study is among the first to chronicle the severity and type of pain that sufferers endure.

In total, 35 genotyped US patients with PC consented to clinical assessment, which included 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, and vibration detection threshold.

Significant pain in patients with PC was confirmed, as indicated by mean BPI severity and QoL impairment, as indicated by mean EQ-5D index of 0.69 ± 0.18. More than half the patients (62%) experienced neuropathic pain, with 38% experiencing nociceptive pain. 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).

The study authors noted that very few of the study participants were receiving analgesic therapy appropriate for neuropathic pain.