Understanding common nail disorders, how to treat them, and when to refer to a dermatology specialist are essential skills for the primary-care clinician. The ability to properly diagnose the following five common nail disorders not only ensures proper treatment but may help you avoid potential malpractice as well.

Onychomycosis (tinea unguium and Candida onychia)

Clinical presentation: Infection of the nail by a dermatophyte or yeast can cause nail discoloration (typically brown or yellow) (Figure 1), onycholysis with or without subungual debris, nail-plate/nail-bed thickening, and ridging and/or pitting of the nail plate.

Background: Onychomycosis is the most common nail disorder, affecting 2%-13% of Americans. The prevalence of this disease is higher in men and in elderly, diabetic, and immunocompromised patients. Prognosis is better with fingernail than toenail involvement; however, 80% of cases involve the feet. An overwhelming majority of cases (approximately 90%) are caused by the dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes. There are three subtypes of tinea unguium depending on the location of the infection. Candida albicans is a less common causative agent and predominantly affects the fingernails. Infections by any of these agents are very difficult to cure permanently.

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Differential diagnosis: Diagnosis is made by KOH prep (tinea is identified by the presence of hyphae, while Candida shows budding yeasts and pseudohyphae). Fungal culture and histologic examination using periodic acid-Schiff stain is the most sensitive diagnostic approach. Psoriasis, eczema, chronic onycholysis, lichen planus, alopecia areata, chronic paronychia, hemorrhage/trauma, aging, pincer-nail dystrophy, yellow-nail syndrome, subungual malignant melanoma, and subungual squamous cell carcinoma are among the differential diagnoses.

Treatment: Both oral and topical medications are used to treat onychomycosis. With superficial disease, topical ciclopirox is effective against dermatophytes and C. albicans, the yeast that accounts for 70% of Candida onychia. Ciclopirox is painted on the nail plate daily, layer upon layer. The layers are then removed with alcohol or nail polish remover every seven days. Daily applications are repeated until the infection clears. This can take six to nine months. The treatment has both anti-inflammatory and antibacterial properties and is up to 30% effective.