Can You Nail the Diagnosis? (It’s Not Fungal)

DISCUSSION
All these findings add up to the diagnosis of psoriasis vulgaris, or common psoriasis, a disease that affects almost 3% of the US population and is far less common in persons with darker skin. This inflammatory condition, thought to be of autoimmune origin, manifested in predictable ways in this patient, who most likely inherited the genetic predisposition for the disease.

Although numerous related chromosomal abnormalities have been identified, environmental factors often play a role in psoriasis as well. These include antecedent strep infection, stress, smoking, obesity, alcohol intake, and use of certain medications (eg, beta-blockers, lithium).

Psoriasis is known to affect nails. The changes in this patient are classic: onycholysis (separation of the nail plate from the nail bed), deformed nails (known as dystrophy), yellow-brown discoloration (so-called oil spotting), and often, splinter hemorrhages. Nail pitting, though not seen in this case, is also common.

For some psoriasis patients, nail involvement is the sole manifestation of the disease. But more often, observing these nail changes prompts the provider to look elsewhere for corroborative findings, of which periumbilical and upper intergluteal involvement are typical.

Seen in a diagnostic vacuum, such nail changes are often diagnosed as “fungal infection.” This overlooks the fact that fungal infection is far less common in the fingernails than in toenails. In fact, there are several other items in the differential for nail changes, including lichen planus, eczema, and chronic candidal paronychia.

Had fungal infection (onychomycosis) been a serious possibility, culture or histologic examination of a sample of nail plate could have been confirmatory. First, though, the other items in the differential should have been considered. (I’ve said it before, in a variety of contexts: If your only explanation for discolored and misshapen nails is fungal infection, that’s a problem.)

This patient’s skin disease was initially treated with topical steroids. However, due to his joint symptoms and the possibility of psoriatic arthropathy, he was also referred to rheumatology. It’s entirely possible that he’ll be prescribed a biologic, which will eliminate his otherwise-problematic-to-treat nail psoriasis.

TAKE-HOME LEARNING POINTS
• Since fungal infection of the fingernails is distinctly uncommon, other items in the differential should be considered in such cases.

• Other potential diagnostic explanations for nail changes include lichen planus, eczema, and chronic candidal paronychia.

• Nail changes can be the sole manifestation of psoriasis in a given patient.

• Evaluation should include other areas of involvement that exhibit “classic” signs of psoriasis, including extensor surfaces and periumbilical and upper intergluteal skin.