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Nail disease occurs in approximately 50% of individuals with psoriasis, with a lifetime incidence of 80-90%.[1] Involvement of the nail in psoriasis can show a wide range of dystrophies, and causes significant morbidity in terms of pain and interference with function as well as cosmetic appearance.[2] Despite this, treatment of nail psoriasis is often overlooked and good evidence regarding optimal management of psoriatic nail dystrophies is much more limited than for skin involvement.[3,4] This makes decisions regarding therapy for nail psoriasis difficult and often unsatisfactory.
1. Clinical Presentation
1.1 Nail Pitting
Nail pits are depressions in the nail plate (figure 1), often deeper in psoriasis than in other conditions, such as lichen planus and alopecia areata.[3,5]
Fig. 1 Nail pitting in a patient with psoriasis. [Figure omitted.]
In psoriasis, nests of parakeratotic cells within the stratum corneum of the proximal nail matrix occur, altering normal keratinization. As the parakeratotic cells are shed with growth of the nail plate, a superficial defect or 'pit' is left in the nail plate.[3]
1.2 Onycholysis
Psoriasis affecting the nail bed shows parakeratosis, with thickening of the stratum corneum and acanthosis. Clinically, this can be seen as discolouration of the nail bed, sometimes referred to as having a 'salmon spot' or 'oil drop' appearance.
Desquamation of parakeratotic cells at the hyponychium leads to onycholysis, seen as a white discolouration as a result of the loss of adherence between the nail plate and nail bed (figure 2).[3] This may provide a portal of entry for bacteria and fungi, which can lead to infection.[1,3,5]
Fig. 2 Onycholysis in a patient with psoriasis. [Figure omitted.]
1.3 Subungual Hyperkeratosis
Nail bed hyperproliferation with accumulation of keratinocytes under the nail results in subungual hyperkeratosis (figure 3). More commonly in psoriasis, this is seen as a white colour, while in other conditions and less frequently in psoriasis, a yellow and rather greasy appearance may be seen, possibly due to deposition of serum or a serum glycoprotein, and a more pronounced inflammatory response.[3]
Fig. 3 Subungual hyperkeratosis in a patient with psoriasis. [Figure omitted.]
1.4 Splinter Haemorrhages
Injury to the capillaries in the longitudinal epidermal-dermal ridges manifests clinically as splinter haemorrhages. These are most commonly precipitated by trauma, but are frequent in psoriasis where nail plate changes...