Title of paper: Chronic pain in Pachyonychia Congenita: evidence for neuropathic origin Authors: S. Brill1, E. Sprecher2, F.J.D. Smith3, N. Geva4, H. Gruener4, H. Nahman-Averbuch5, R. Defrin4   1Center for Pain Medicine, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel. 2Department of Dermatology, Tel-Aviv Sourasky Medical Center and Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv Israel. 3Pachyonychia Congenita Project, P.O. Box 17850, Holladay, UT, 84117-0850, USA. 4Department of Physical Therapy, Sackler Faculty of Medicine & Sagol School of Neuroscience, Tel-Aviv University, Tel-Aviv, 69978, Israel. 5Department of Anesthesia, Cincinnati Children's Hospital Medical Center, Ohio, USA British Journal of Dermatology. DOI: 10.111/bjd.16217

Introduction (1) What’s already known? Chronic pain is the most prominent and debilitating complaint in Pachyonychia congenita (PC) The origin of the pain is not established hence also an appropriate intervention

Introduction (2) Previous histological studies found alterations in sensory innervation The current study has performed, for the first time, systematic evaluation of somatosensory function and pain modulation using quantitative sensory testing (QST) and characterized the clinical features of the chronic pain

Methods (1) Patients with PC (n=62) and controls (n=45) completed the McGill pain questionnaire and Douleur Neuropathique-4 (DN4) questionnaire.

Methods (2) Sensory testing included: warm detection and pain thresholds, pathological sensations, conditioned pain modulation (CPM) and temporal summation of pain (TSP).

Results (1) Hypoesthesia along with mechanical hyperalgesia and allodynia in the painful body regions Causative mutation and gene harboring were not associated with any of these features

Results (2) The clinical and physiological characteristics of the pain suggest a possible neuropathic origin Neuropathic pain medications may be beneficial for PC patients

Discussion (1) What does this study add? Although thermal and mechanical hypoesthesia may result from thicker skin, its presentation in painful body regions along with mechanical hyperalgesia and allodynia point towards the possibility of neuropathic changes in PC.

Discussion (2) The clinical features and DN4 scores support this possibility and therefore neuropathic pain medications may be beneficial for PC patients.

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