Various Presentations 1,2,3,4,5
Pitting is the commonest symptom of nail psoriasis. Pits usually affect the fingernails more commonly than the toenails. They are superficial depressions in the nail plate that indicate abnormalities in the proximal nail matrix (where the nail grows from under the cuticle). Psoriasis affecting the proximal nail matrix disrupts the keratinization of its stratum corneum by parakeratotic cells. Keratinization is the process by which epithelial cells become filled with keratin protein filaments, die, and form tough, resistant structures such as the skin, nails and hair. Pitting results when the keratinization process has been disrupted and the structure of the nail has been compromised allowing some of the cells, as the nail grows and becomes exposed, to be sloughed off forming scattered and coarse pits. Pitting may be arranged in transverse (side to side) or longitudinal rows or it may be randomly scattered. They may be shallow or large to the point of leaving a punched out hole in the nail plate. This is known as elkonyxis.
Clustered Scattered Linear
Transverse grooves (also known as Beau lines) are formed in the same way as pits. This occurs when the psoriatic lesion affects a wider area of the nail matrix.
Subungual hyperkeratosis (Nail plate thickening) and crumbling
An extensive involvement of the entire nail matrix affecting the toenails more frequently than the fingernails. It results from the lifting of the nail plate off the nail bed due to the build-up of cells that have not undergone desquamation (shedding). The resulting accumulated tissue is friable (soft and crumbling) which is susceptible to infection by fungal dermatophytes e.g. Candida albicans (C. albicans) and pseudomonas aeruginosa, leading to either yellow/green discoloration.
Crumbling Nail Plate
Leukonychia consists of areas of white nail plate due circumscribed focus of trapped parakeratotic cells within the body of the nail plate. Punctate Leukonychia is characterized by white spots 1-3 mm in diameter occurring singly or in groups and almost exclusively appear on the finger nails.
Transverse leukonychia Punctate leukonychia
Subacute or chronic paronychia
Psoriatic paronychia usually develops when the periungual skin (around the cuticle) is affected by psoriasis, but it is also commonly seen in psoriatic arthritis with nail involvement. The chronic inflammation causes thickening of the free edge of the proximal nail fold with consecutive loss of cuticle and the attachment of the nail fold’s ventral surface to the underlying nail plate. This allows foreign material such as dirt, microorganisms, or allergenic substances to enter the space beneath the nail fold where they may aggravate inflammation.
Acropustulosis is associated with pustular psoriasis and can involve one or all of the digits on the feet and hands. Pustulation of the nail bed and its growth site (matrix) may result in onychodystrophy (malformation) and anonychia (loss of nail). It may also occur as either a part of palmoplantar pustulosis, or acrodermatitis continua of Hallopeau. Usually, there is erythema (redness), swelling and severe discomfort of the entire digit or at the end of the digit. Resorptive osteolysis (resorption of the bone) of the finger or toes may also occur.
Splinter Haemorrhages and Salmon Spots
Splinter haemorrhages are small linear blackish streaks, about 2-3 mm long, arranged at the distal end of a nail plate. They are caused by the rupture of blood vessels and tracking of the blood along the longitudinal furrows beneath the nail plate. Salmon Spots, also known as “Oil Spots” are a translucent yellowish-red discoloration in the nail bed and can be a small rounded spot or a largish odd shaped spot.
Splinter Haemorrhages Salmon Patch
Onycholysis (separation of nail plate from nail bed)
It usually starts at the tip and/or the side(s) of the nail and works backwards. It normally appears white, but occasionally may also appear yellowish. Secondary fungal infections are common.
Secondary fungal infections, Onychomycosis, may cause a brownish, blackish or even greenish discolouration.
Onychomycosis is caused by dermatophytes, yeast (C. albicans) and moulds (e.g. Pseudomonas) and is the most common nail disease worldwide with between 6 -30% of the population affected, in PsN up to 70% of sufferers have a secondary fungal infection. Psoriasis often leads to abnormal morphology of the nails. Nails, damaged by psoriasis, lose their natural protective barrier and are therefore more susceptible to fungal infections. Researchers have found that dermatophytes more often cause toenail onychomycosis. Yeasts were isolated in a higher percentage from fingernails. The most common pathogens are Trichophyton rubrum, Trichophyton mentagrophytes and C. albicans. A correlation was observed between psoriatic change of fingernail plate – Nail Psoriasis Severity Index (NAPSI) and positive mycology.5
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