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Nail lesions in palmoplantar pustulosis are not significantly associated with distal interphalangeal arthritis

Dear Editor, Palmoplantar pustulosis (PPP) is closely related to psoriasis, either plaque type or pustular type. Although PPP and psoriasis share the pathogenesis in many aspects, there are several differences.1 In psoriasis, nail lesions are closely related to distal interphalangeal (DIP) arthritis. We examined the relationship between nail lesions and DIP arthritis in patients with PPP. After obtaining the approval of the institutional review board of Fukushima Medical University, we retrospectively examined 166 PPP patients, who visited our department between 2007 and 2020. Among them, nail involvement was observed in 50 patients (30.1%). Pustulotic arthroosteitis (PAO) was observed in 53 patients (31.9%), as was consistent with previous data.2,3 Among the 50 patients with nail lesions, 26 patients complained of joint pain and 16 of those 26 patients were diagnosed with PAO involving the digits (n = 3; two DIP joints and one proximal interphalangeal [PIP] joints), as well as other sites such as anterior chest wall, shoulders, hip, knees, and elbows. The comparison of frequency of PAO between the patients with and without nail involvement did not show any significant difference (16/50 [32.0%] vs 37/116 [31.9%]). The two patients with DIP arthritis, who were treated with tumor necrosis factor inhibitors, exhibited nail pitting (n = 1), onycholysis (n = 2), subungual pustulosis (n = 1), white scales (n = 1), and onychodystrophy (n = 2). Nail Psoriasis Severity Index score was 8 in both cases. Among the 116 patients without nail involvement, DIP arthritis was observed in one patient. There was no significant difference in the frequency of DIP arthritis between the patients with (2/50) and without (1/116) nail involvement. In conclusion, nail involvement was not significantly associated with manifestation in either DIP joints or other joints in the patients with PPP (Table 1). The frequency of nail involvement in PPP was 30.1% in the current study, whereas it is more common in psoriasis patients with a frequency of around 60%.4 In peripheraltype psoriatic arthritis (PsA), DIP arthritis frequently accompanies nail lesions, because DIP extensor tendon enthesis and nail matrix are closely located anatomically.5 Another possibility regarding concurrent involvement of DIP joint and nail matrix is due to Köbner/deep Köbner phenomenon caused by frequent use of the fingertips.5 In the current study, two patients had DIP arthritis, both of whom were confirmed by bone scintigraphy and magnetic resonance imaging, and those two patients had nail lesions, suggesting that DIP joint manifestation is related to nail involvement in PAO, as is observed in PsA. By contrast, among the 50 PPP patients with nail lesions, only two patients had DIP arthritis, indicating that very few PPP patients with nail lesions further develop DIP arthritis. It has been reported that nail psoriasis is related to PsA; however, our results showed that the presence of nail lesions in PPP did not correlate with PAO. Inflammation of nail matrix in PPP may not have a capacity to affect the DIP joints. Although the precise mechanism in unknown, our results suggest a different significance of nail lesions between PsA and PAO, which may reflect a different nature of both diseases.