Nailing the diagnosis of psoriatic arthritis
Oct. 30, 2017
Nail psoriasis (NP) has a profound psychosocial effect on a patient’s life. Aside from its physical appearance, NP may be a clue to associated psoriatic arthritis (PA).
Approximately 40% of patients with psoriasis display nail disease; it is 80% for those with PA. The most common nail sign in psoriasis is pitting, which affects approximately 68% of patients. Other characteristic changes include onycholysis, subungual hyperkeratosis, trachyonychia, “oil drops,” splinter hemorrhages, red spots in the lunula, leukonychia, and transverse grooves (Beau lines). All of these changes, with the exception of transverse grooves, are used in measuring NAPSI (Nail Psoriasis Severity Index). (1,2)
In a study of 313 children with psoriasis, nails were involved in 101 (32.3%). The most common features were pitting (69.1%), onycholysis (28.7%), Beau lines (25.5%), oil drop (19.1%), paronychia (17.0%), pachyonychia (13.8%), leukonychia (9.6%), and splinter hemorrhages (4.3%). All the following features were statistically significant: pitting was more frequent on fingernails; onycholysis and pachyonychia were more frequent on toenails. (3)
The differential diagnosis of NP includes dermatophytosis, Candidiasis, crusted scabies, Darier disease, pityriasis rubra pilaris, lichen planus, twenty nail dystrophy, alopecia areata and pachyonychia congenita.
According to McArdle et al, between 6 and 48% of patients with psoriasis may develop PA. The most recently developed criteria for PA are the CASPAR (Classification Criteria for Psoriatic Arthritis Group) criteria in which a patient must have inflammatory articular disease (joint, spine, or entheseal) with ≥ 3 points from the following 5 categories (a = 2 points) (4):
(1) Evidence of current psoriasis [a] (psoriatic skin or scalp disease judged by a rheumatologist or dermatologist), a personal history of psoriasis or a family history of psoriasis (in a first or second-degree relative)
(2) Typical nail dystrophy including onycholysis, pitting and hyperkeratosis observed on current physical examination
(3) A negative test result for the presence of rheumatoid factor by any method except latex but preferably by enzyme-linked immunosorbent assay or nephelometry, according to the local laboratory reference range
(4) Either current dactylitis, defined as swelling of an entire digit, or a history of dactylitis recorded by a rheumatologist
(5) Radiographic evidence of juxta articular new bone formation, appearing as ill-defined ossification near joint margins (but excluding osteophyte formation) on plain radiographs of the hand or foot
Differentiating PA from other inflammatory arthritides (IA) is essential as therapeutic approaches differ. While certain drugs such as methotrexate or TNF inhibitors may help both PA and rheumatoid arthritis, avoidance of hydroxychloroquine or steroids would be appropriate for PA patients. Unfortunately, there are no diagnostic tests that clearly differentiate PA from IA — the diagnosis of PS depends on its recognition by astute clinicians.
Zenke et performed a retrospective analysis of 118 patients with PA and 974 patients with psoriasis without arthritis. The incidence of nail involvement in patients with PA was 67.6%. Female sex, presence of transverse grooves, onycholysis, and splinter hemorrhages were significantly related to PA, with transverse grooves demonstrating the strongest significant association (odds ratio, 5.01). Importantly, the presence of transverse grooves was strongly related to both distal interphalangeal arthritis and enthesitis. The authors concluded that the presence of transverse grooves is significantly associated with PA and may be associated with distal interphalangeal arthritis and enthesitis. (5)
Should these findings be verified by subsequent studies, this simple clinical observation would be most useful in determining which patients have PA; this would allow appropriate systemic therapy to be instituted without delay. What I don’t understand is why the association of transverse grooves and PA was not recognized years ago. Regardless, now that this has come to our attention, until other studies either confirm or refute this intriguing association, we should consider assessing such patients with transverse groove for PA.
1. Sobolowski P, et al. Nail involvement in psoriatic arthritis. Reumatologia 2017; 55: 131-5.
2. Zenke Y, et al. Nail findings in patients with psoriatic arthritis: A cross-sectional study with special reference to transverse grooves. J Am Acad Dermatol 2017; 77: 863-7.
3. Pourchot D, et al. Nail psoriasis: A systematic evaluation in 313 children with psoriasis. Pediatr Dermatol 2017; 34: 58-63.
4. McArdle A, et al. Clinical features of psoriatic arthritis: A comprehensive review of unmet clinical needs. Clin Rev Allergy Immunol 2017; Jul 27 [Epub ahead of print]
5. Zenke Y, et al. Nail findings in patients with psoriatic arthritis: A cross-sectional study with special reference to transverse grooves. J Am Acad Dermatol 2017; 77: 863-7.
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