Onychomycosis: Understanding The Disease And Its Consequences
Patrick S. J. McElgunn, MD, FRCPC*
Onychomycosis is a chronic infection of the nail plate and nail bed (Figure 1) by dermatophytes, yeasts, and opportunistic fungi. Commonly considered as "just a cosmetic problem," onychomycosis can lead to serious, long-term, and permanent damage to the digits. The disease is approximately 20 times more common in toenails than in fingernails.1,2
Onychomycosis is contagious; if not properly treated and managed, it easily can spread to other toes, other body areas, and other people. In patients with diabetes and in those patients with human immuno-deficiency virus (HIV), the fungal infection can become a portal for a secondary superinfection with bacteria.
Onychomycosis can be painful. A quality-of-life study showed that almost 50% of patients with onychomycosis have pain. Another 40% of patients describe nail pressure, and 38% have some discomfort when wearing shoes. Seventy-five percent of patients have difficulty trimming their toenails, and the disease causes significant embarrassment for patients, such as the inability to wear sandals or to participate in sports.3
Onychomycosis is underdiagnosed and undertreated. It is estimated that approximately 10% of the US population has onychomycosis.1,4 Evidence points to an increasing prevalence as the population ages and an increasing overall prevalence. Up to 60% of people who are 60 years and older are reported to have onychomycosis.5 The incidence is also higher in men, smokers, and in those patients with peripheral artery disease or HIV.6
The infection often begins as tinea pedis (dermatophytosis of the feet, particularly between the digits and on the soles), which spreads underneath the nail plate and becomes onychomycosis. A warm humid environment caused by shoes can help promote growth of the organism, and pressure from tight-fitting shoes can break the seal between the nail plate and the nail bed at the distal hyponychium, allowing subungual (beneath the nail) invasion. Tinea pedis can be treated topically, but if the nail infection is not treated, tinea pedis will likely recur. Chronic infection also can disrupt the skin, allowing for easier secondary bacterial infection. It can be a source for tinea to spread to other body areas or other people.
Trichophyton rubrum (a dermatophyte) is the primary pathogen for onychomycosis, accounting for more than 90% of infections (see "The Majority of Onychomycosis Pathogens" sidebar).7-10 Candida molds and other molds constitute most of the remaining 10%.
Onychomycosis can be divided into 4 clinical types: distal subungual onychomycosis (DSO), proximal subungual onychomycosis (PSO), white superficial onychomycosis (WSO), and candidal onychomycosis. DSO is the most common. More than 90% of cases are caused by T. rubrum, but other nondermatophyte molds may be involved, such as Aspergillus, Scopulariopsis, Scytalidium, and Fusarium. DSO starts with the invasion of the lateral or distal edges of the nail bed and the underside of the nail plate, beginning at the hyponychium (Figure 2). The localized mild inflammation and excess growth of the nail bed is in response to the infection and causes subungual hyperkeratosis (excess growth of the corneous layer of the skin). As the debris builds, the nail plate is lifted off its bed, beginning distally and proceeding proximally, thus exposing more of the nail bed to future infection. Lifting of the nail plate from the nail bed is referred to as onycholysis. The nail has a yellowish-brown appearance.1
Proximal subungual onychomycosis is the least common type of onychomycosis in clinical practice, but it is most commonly seen in patients with HIV. PSO is considered an early marker of HIV infection. The fungus invades through the proximal nail fold at the cuticle area, penetrates the newly formed nail plate, proceeds distally, and eventually penetrates all nail layers and the entire nail. Beau's lines (transverse depressions) may also appear in the nail plate. The end result is total dystrophic onychomycosis with a convex, irregular, and rough nail. Clinical presentation usually is a white or whitish brown area on the proximal nail plate, along with subungual hyperkeratosis, proximal onycholysis, leukonychia (whitish discoloration of nail), and destruction of the proximal nail plate (Figure 3).11
White superficial onychomycosis is much less common than distal subungual onychomycosis, is confined to the nail plate, and usually is caused by Trichophyton mentagrophytes. As its name implies, WSO is a superficial infection of the nail plate, seen as distinct white islands (Figure 4). As the infection progresses, these islands coalesce and the nail becomes soft, flaky, and crumbly. Because WSO is a superficial infection, inflammation usually is minimal.
Candidal onychomycosis is rare in toenails. It may be more common in patients with diabetes, who may have coexisting mucocutaneous candidiasis.12,13 Infection starts at the distal nail, invading the ventral surface in the hyponychium area, and spreads rapidly to involve the entire nail plate. The disease can penetrate the nail plate after it has infected the nail's surrounding soft tissue. Candidal onychomycosis is less hyperkeratotic than derm-atophytic onychomycosis. The infected nail usually has an opaque, rough, or furrowed appearance with a brownish or brownish-yellowish color (Figure 5).
Effective management of onychomycosis requires patient education and appropriate patient expectations. Physicians, nurse practitioners, and physician assistants should be prepared to continually educate their patients on this infection. Treatment is long term and patients may lose their enthusiasm for the care and involvement required to manage this disease.
Patients should understand that onychomycosis is an infection, not a normal consequence of aging. There are several important reasons to treat this disease: Pain and discomfort can become predominant quality-of-life issues, onychomycosis can act as a source of tinea to other body areas or other family members, and the disease can lead to much more serious consequences in patients with diabetes mellitus, such as nail removal, secondary bacterial infection, and increased risk of amputation.
Patients beginning a treatment plan must realize that treatment is a long process—often extending for longer than 1 year and involving maintenance therapy. It is paramount that patients understand the difference between cure and control of this condition. Cost issues may arise, depending on the patient's insurance, and may affect treatment decisions. Treatment costs may offset the long-term "costs" of nontreatment.
The primary care provider frequently is the first healthcare provider seen by a patient with onychomycosis. Primary care providers should be aware of the forms of onychomycosis, the patient populations frequently affected by it and, perhaps most importantly, the serious consequences of the disease if left untreated. Primary care providers can diagnose and initiate treatment for this disease, but they should also work in conjunction with a specialist to ensure optimal long-term care.
This issue of Advanced Studies in Medicine presents several case studies of onychomycosis and discussions of each case by 2 physicians with extensive experience in treating onychomycosis in different patient populations. Dr Warren Joseph discusses onychomycosis in adults—general populations and in special populations, such as patients with HIV or diabetes mellitus and elderly patients. Dr Sheila Fallon Friedlander discusses 2 cases of pediatric onychomycosis, including diagnosis, prevalence in the pediatric population, and unique issues regarding this disease in children, such as the role of infected family members and proper foot hygiene. Both physicians provide important reviews of the currently available treatments and the best approaches to diagnosis and management, especially for primary care physicians.
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*Assistant Professor, Department of Dermatology, Johns Hopkins University School of Medicine, Director of Cosmetic Dermatology and Laser Surgery, Johns Hopkins Dermatology and Cosmetic Center, Lutherville, Maryland.
Address correspondence to: Patrick S. J. McElgunn, MD, FRCPC, Assistant Professor, Department of Dermatology, Johns Hopkins University School of Medicine, Director of Cosmetic Dermatology and Laser Surgery, Johns Hopkins Dermatology and Cosmetic Center, Green Spring Station, 10755 Falls Road, Pavilion 1, Suite 350, Lutherville, MD 21093.