SG07 Evaluation of the Foot Function Index in pachyonychia congenita

• Published in: British journal of dermatology (1951) Vol. 191; no. Supplement_1; p. i184
• Main Authors: Oldham, Jaimie, Stuart, Beth, McCarthy, Rebecca, Schwartz, Janice, Evans, Holly, Hansen, David, O’Toole, Edel
• Format: Journal Article
• Language: English
• Published: 28-06-2024
• ISSN: 0007-0963; 1365-2133
• DOI: 10.1093/bjd/ljae090.389

Pachyonychia congenita (PC) is a rare autosomal dominant disorder caused by variants in the keratin genes KRT6A, KRT6B, KRT6C, KRT16 or KRT17 (PC-K6a, PC-K6b, PC-K6c, PC-K16, PC-K17). All subtypes are associated with plantar calluses, and 98% with plantar pain. Our aim was to assess the utility of the Foot Function Index (FFI) in quantifying the impact of painful calluses on function in PC. The FFI is a self-administered questionnaire composed of 23 questions. It produces a total score and three subscale scores (activity limitation, disability and pain), each of which range from 0% (no effect) to 100% (maximum effect). Patients from the International Pachyonychia Congenita Research Registry (IPCRR) with confirmed PC were asked to complete the FFI three times over 3 months. As well as the FFI, respondents were asked to document the peak temperature that day and their sex. Data were collected from the IPCRR for age and gene variants. In total, 389 responses were received from 211 patients with PC (125 female, 69 male, 17 question not answered). Their age ranged from 6 to 85 years. Genotypes included PC-K6a (62), PC-K6b (29), PC-K6C (11), PC-K16 (95) and PC-K17 (14). The mean score across different timepoint observations was consistent, with overall mean scores of 40.2% (SD 19.8), 40.6% (SD 19.0) and 38.1% (SD 17.0) across the first, second and third measurements, respectively. All groups have lower overall scores than the KRT16 group (44.4%, SD 17.9), but that difference is only statistically significant for the KRT6B group [−9.93%, 95% confidence interval (CI) −17.9 to −1.96]. The disability score and the activity limitation score also showed lower scores in the other gene groups compared with KRT16 (disability 45.3%, SD 20.8; activity limitation 25.2%, SD 17.7), but only the KRT6B group showed statistically significantly lower scores: −13.0%, 95% CI −21.7 to −2.22 for disability, and −8.25%, 95% CI −15.7 to −0.82 for activity limitation. For the pain score, all gene groups had a significantly lower score than KRT16 (54.1%, SD 20.3), apart from KRT6C. The values were KRT6A −8.99% (95% CI −15.7 to −2.3), KRT6B −12.5% (95% CI −21.3 to −3.8) and KRT17 −14.1% (95% CI −25.8 to −2.4). There was no clear relationship between age, temperature or sex and any FFI score. Overall, the results show a significant impact of PC on foot function. The results suggest that some genotypes have a bigger impact on foot function than others, particularly KRT16 variants. The FFI may be a suitable patient-reported outcome measure in PC clinical trials.