Clinical presentation: Pitting, nonspecific onycholysis (lifting of the nail from the nail bed), hyperkeratosis (thick nails), and yellowish-brown spots under the nail plate should prompt consideration of nail psoriasis (Figure 3). The yellow-brown spots, also known as “oil spots,” are pathognomonic.

Background: One quarter of patients with cutaneous psoriasis also have fingernail and toenail involvement. This diagnosis is sometimes missed when there is no clear history of cutaneous psoriasis. Be sure to ask patients presenting with suspicious nail signs about a family history of psoriasis and to examine their skin in its entirety. I recently saw a 13-year-old boy for a second opinion. The boy’s mother had been told by her son’s primary-care provider that the diagnosis was nail psoriasis. She only believed the diagnosis when I pointed out that the plaques on the boy’s scalp were not dandruff but psoriasis.

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Differential diagnosis: Perform a culture to rule out fungal involvement.

Treatment: Nail psoriasis can be difficult to treat. Topical steroids provide poor penetration. Repeated triamcinolone injections into the nail matrix may help, but are very painful and do not provide long-term remission. Biologics (e.g., etanercept [Enbrel], adalimumab [Humira], or infliximab [Remicade]) are systemic agents used to control moderate-to-severe psoriasis and psoriatic arthritis. These agents can also result in remission of nail disease. Improvement is slow, and complete resolution can take as long as a year. Biologics are expensive and are usually prescribed only by dermatologists or rheumatologists. If the patient desires treatment for the nails, a dermatologic referral is most appropriate.

Subungual squamous cell carcinoma (in situ or invasive)

Clinical presentation: Subungual squamous cell carcinoma (SCC) in situ presents as flesh-colored or hyperpigmented verrucous papules or plaques with either keratosis or hyperkeratosis (Figure 4). Onycholysis can occur. Invasive SCC can begin as bone pain but is most commonly depicted as a slow-growing solitary subungual or periungual nodule that ulcerates and/or bleeds and likely destroys the nail.

Background: Subungual SCC is the most common malignant tumor of the nail. Fingers are more likely to be involved (especially the first and fourth digits). Metastasis to the bone occurs 20%-55% of the time. Proximal and lateral nail plates, the nail matrix, and the hyponychium are affected. Human papillomavirus (HPV) type 16, 18, 34, or 35 is detected in more than 60% of cases. HIV-positive patients are especially susceptible to developing HPV-associated SCC. Cancer in this area is rare and usually a result of prior radiation therapy, but the prognosis is good when compared with that of SCC in other cutaneous sites. 

Differential diagnosis: Rule out onychomycosis, verruca vulgaris, and paronychia.

Treatment: Nail biopsy is necessary to make the diagnosis of subungual SCC. Mohs micrographic surgery is employed with noninvasive disease; the cure rate is around 96%. When bone is involved, amputation of the affected digit and/or radiation therapy can be used to destroy the unresectable tumor. If you are faced with a nail problem or lesion that won’t go away, consider a biopsy to rule out underlying subungual SCC.