CASE #1: Onychomycosis
Onychomycosis is the most common disease of nails, with a prevalence of up to 14% in Western adult populations. Whereas tinea unguium refers strictly to dermatophyte fungal infection of the nail plate, onychomycosis includes dermatophyte, nondermatophyte, and yeast infection of the nail.
Patients particularly at risk for this disease include the immunosuppressed and those with peripheral vascular disease, Down’s syndrome, or a history of nail trauma. Because the cell-mediated component of host defense is most involved in preventing fungal infection, it is patients with depressed T-cell counts (e.g. HIV/AIDS patients) rather than those with defects in humoral immunity that are most susceptible to onychomycosis. Tinea pedis complicates a third of all cases of onychomycosis and can serve as a reservoir for recurrent nail infections.1
Four clinical types of onychomycosis exist. The most common form is distal-lateral subungual onychomycosis, a result of distal nail bed and/or hyponychium invasion. The infection often starts distally with a whitish to brown-yellow opacification that can progress to include the entire nail. Proximal subungual onychomycosis (more commonly found in immunosuppressed patients) begins and travels in the opposite direction, usually appearing as an infection beneath the nail. White superficial onychomycosis (most commonly seen in children) is the result of direct invasion of the nail plate from above. This form can appear anywhere on the nail plate as powdery white, sharply bordered patches. The final form, candidal onychomycosis, is unique in that the pseudohyphae of the Candida species display invasion through the entire thickness of the nail plate.
The diagnostic standard for onychomycosis is positive microscopy and culture of nail clippings with subungual debris.2 Periodic acid-Schiff (PAS) examination of nail clippings is the most sensitive test, while culture is the most specific. A cost-effective alternative to PAS examination is KOH preparation with chorazol black E staining, which yields a 94% positive predictive value. In addition, such clinical clues as nearby redness with peripheral scaling and central clearing—evidence of tinea pedis—make the diagnosis of onychomycosis more likely. Despite the high sensitivity of microscopy, many cases exist in which the microscopy is negative despite the high clinical suspicion for fungal nail disease. Conversely, many times a positive microscopic result yields a negative culture.
Given these pitfalls in diagnosis, several guidelines can be followed.3 First, always consider isolation of a dermatophyte in culture as a pathogen. Next, only consider a nondermatophyte isolated in culture to be a pathogen if hyphae, spores, or yeast are identified on microscopy. Finally, to confirm a nondermatophyte infection, attempted repeat isolation is recommended. At least five of 20 inocula should have nondermatophyte present without evidence of dermatophyte incidence.
Practitioners often prescribe treatment without confirmatory sampling. This is a potential drawback as onychomycosis accounts for only 50% of dystrophic nails. The most likely alternative diagnoses are psoriasis and chronic trauma. Patients with psoriasis will usually report a history of rash on the elbows and knees and, more rarely, a history of associated arthritis, which can feature nail pitting—a finding not typical of onychomycosis. A history of chronic trauma can easily be elicited from the patient and is usually associated with a single nail. Other diagnoses to consider are lichen planus, Darier disease, acquired and congenital leukonychias, yellow-nail syndrome, and onychogryphosis. Lichen planus is suggested by atrophy and nail scarring that can result in loss of finger dexterity in association with the characteristic pruritic, planar, purple, polygonal papules. Nails in yellow-nail syndrome, a condition commonly associated with such respiratory disorders as chronic sinusitis, bronchiectasis, and lymphedema, become yellow and grow slowly.
It is important to rule out periungual squamous cell carcinoma, Norwegian scabies, and Reiter’s syndrome, as significant morbidity can be prevented with early diagnosis. This requires a careful history with attention to such exposures as high-risk sexual activity and intense pruritis (in cases of Norweigan scabies) or recent GI illness (in cases of Reiter’s syndrome). Perigungual squamous cell carcinoma usually affects a single nail and typically mimics a wart but can also resemble chronic paronychia with more pronounced soft-tissue changes than are found in onychomycosis; a biopsy is necessary to make a definitive diagnosis.
Onychomycosis treatment is guided by whether the nail matrix area is involved. If the matrix is spared, topical treatment with ciclopirox nail lacquer along with careful nail debridement is effective. Otherwise, systemic treatment offers the best chance for cure. In one large meta-analysis, terbinafine was found to be the most effective single-agent treatment for onychomycosis, with a cure rate of 76% compared with 60% for griseofulvin and 48% for fluconazole. The most common side effects of terbinafine include nausea, diarrhea, and mild abdominal pain. Recently, combination therapy has been shown to be more effective than single-agent treatment, with one study demonstrating terbinafine combined with ciclopirox nail lacquer achieving mycologic cure of 88% compared with 65% for terbinafine alone. Fluconazole and itraconazole are better suited for treatment of candidal onychomycosis. Debridement and avulsion therapy are two helpful mechanical adjunct treatments. Mechanical debridement can help with painful nails, although it is rarely enough to cure onychomycosis as monotherapy. Partial nail avulsion is preferred over total nail avulsion, as removing the entire nail leads to increased rates of ingrown nails and other irritation reactions.
This patient was given a three-month course of terbinafine 250 mg daily. Six months later, his nails were no longer yellowed or dystrophic.