A recent study published in The Journal of Rheumatology found an association between psoriatic nail dystrophy, particularly onycholysis, and erosive damage at the distal interphalangeal (DIP) joints. Moreover, the association between subungual hyperkeratosis and erosive disease is stronger at the DIP joints than at non-DIP joints. These findings support the anatomical and pathological link between nails and DIP joint disease.

In this retrospective cohort study, the investigators selected individuals with psoriatic arthritis (PsA) from the Bath longitudinal cohort. All the individuals were aged at least 18 years and met the Classification Criteria for PsA. The investigators measured nail disease using the Psoriatic Nail Severity Score (range 0-40 in hands), which documents the presence or absence of pitting, onycholysis, subungual hyperkeratosis, and severe nail destruction.

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The investigators also assessed anteroposterior radiographs of the hands, wrists, and feet taken every 2 years in the Bath cohort of patients with PsA. The presence and severity of erosive disease were graded using the modified Sharp/van der Heijde score or the Ratingen Score. Chi-square tests were performed to examine the association between features of nail dystrophy and radiographic damage in the DIP joints and proximal interphalangeal or metacarpophalangeal joints (non-DIP joints) of the corresponding digits.

There were 134 patients included in this study, with a median age of 53 years and a median disease duration of 7 years. Study investigators found that nail disease was present in 70.1% of participants and affected 25.8% of nails. The most frequent manifestations were onycholysis (24.2%), pitting (22.8%), subungual hyperkeratosis (5.5%), and severe nail deformity (2.8%).


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The most frequent radiographic damage variable was joint space narrowing at both the DIP joints (34.3% of 1340 joints scored) and non-DIP joints (30.2% of 2680 joints scored), followed by osteoproliferation (11.8% and 13.9%, respectively) and erosions (7.8% and 12.6%, respectively). The presence of any form of psoriatic nail dystrophy was associated with erosion at the DIP joints of the corresponding digit (odds ratio [OR], 1.9; 95% CI, 1.23-2.83; P <.004) and this association was primarily driven by the presence of nail onycholysis (OR, 1.72; 95% CI, 1.12-2.62; P =.02). Nail subungal hyperkeratosis was more strongly associated with joint space narrowing, erosions, and osteoproliferation at the corresponding DIP joints compared with non-DIP joints (P <.001). Nail pitting was not associated with erosions or osteoproliferation.

The primary study limitations are the lack of complete longitudinal clinical data, such as the Psoriasis Area and Severity Index Score and Body Surface Area, which may serve as confounders, and the absence of serial radiographic data, which precludes meaningful regression analysis from assessing the effect of nail disease subtypes.

These findings support the studies that demonstrate the anatomical, radiological, and clinical association between psoriatic nail dystrophy and DIP joint disease. The DIP joint damage is a reflection of disease activity in the DIP joint and emphasizes the close anatomical relationship between inflammation in the nail bed-matrix complex and the DIP joints.

Reference

Antony A, Allard A, Rambojun A, et al. Psoriatic nail dystrophy is associated with erosive disease in the distal interphalangeal joints in psoriatic arthritis: a retrospective cohort study [published online March 1, 2019]. J Rheumatol. doi: 10.3899/jrheum.180796