Psoriasis: nail psoriasis

Psoriatic nail dystrophy mainly occurs in patients who also suffer from psoriasis of the skin. Less than 5% of patients have solely psoriasis of the nails. It commonly affects patients with psoriatic arthritis.

This chapter is set out as follows:

• Pitting
• Onycholysis - a yellow / white discoloration where the distal nail plate has separated from the nail bed 
• Subungual hyperkeratosis - thickening of the nail bed
• Oil drop or salmon patch - translucent yellow-red discolouration in the nail bed, resembles a drop of oil under nail plate

• If there is any diagnostic uncertainty samples must be sent for mycology to rule out tinea. It is important to not only include nail clippings but also scrapings from the undersurface of the nail plate, otherwise many cases of tinea will be missed. It must be remembered that psoriasis and tinea of the nails can co-exist

• Treatment of nails is difficult and results are often disappointing. Patients should be encouraged to keep their nails short. The use of nail varnish will not cause harm and can help disguise nail changes

• For troublesome cases the following can be discussed with the patient:

• Distal nail involvement - advise the patient to cut the nail back as far as possible then apply a potent topical steroid, possibly combined with a vitamin D analogue, once a day for a trial period of three months

• More substantial involvement (including proximal nail) - consider referral to dermatology for a trial of triamcinolone injections via Dermojet ®. Systemic agents such as methotrexate are occasionally used but benefit is not guaranteed, and the risk to benefit ratio means that such treatments are not often justified unless the nail changes are severe or the patient also has moderate-severe psoriasis of the skin