For more invasive disease, confirmation of onychomycosis is needed prior to initiation and to obtain insurance coverage of treatment, which is expensive. Terbinafine 250 mg daily over a period of six weeks for fingernails and 12 weeks for toenails is first-line therapy. Because of its lipophilic nature, terbinafine remains in the nail plate for several months post treatment. It has an average success rate of 70% following a three-month regimen. Itraconazole and fluconazole are also effective. All three medications can be dosed daily or in pulsed increments of one week per month for two consecutive months for fingernails or three consecutive months for toenails. Because there is a chance of permanently impaired liver function with these medications, testing should be done before therapy begins, after the first month of therapy, and once therapy is completed.

The best way to prevent onychomycosis is to treat concurrent tinea pedis. Other prevention strategies include wearing foot protection in areas of high traffic or high dermatophyte concentration (swimming pools, locker rooms, spas), drying feet thoroughly, and wearing socks made of absorbent material. 

Chronic paronychia

Clinical presentation: Chronic paronychia (Figure 2) is characterized by erythema and edema of the proximal and lateral nail folds, cuticle loss, separation of the nail from the nail plate, and development of either thin, weak nails that break easily or thick rounded nails. When chronic paronychia becomes infected with Pseudomonas, the nails may appear green and there may be accompanying discharge.

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Background: In acute paronychia, there may be pus or clear signs of infection, but chronic paronychia is considerably more subtle and requires much longer treatment. Chronic paronychia is an inflammatory disorder of the proximal nail fold. Some occupations expose patients to greater risk because of repeated exposure to wet environments (e.g., wait staff or bartender). Repeated minor trauma to the cuticle can allow irritants to further damage the nail. In addition to Pseudomonas, other microorganisms, such as Candida albicans or Staphylococcus aureus, can infect the space between the proximal nail fold and nail plate.

Differential diagnosis: Rule out chronic herpetic infection by performing a viral culture or Tzanck smear. Herpetic infection is more commonly seen in those whose hands come in contact with the oral cavity (e.g., dentists, oral hygienists).

Treatment: The most important element of treatment is protecting the nail from chronic irritation. While this irritation is sometimes occupational, it is often habitual. Patients become accustomed to removing the cuticle themselves or trying to express accumulated fluid from the area. In addition to behavior modifications, topical application of a mixture of triamcinolone 0.1% cream and clotrimazole cream to the nail folds for 6-12 weeks will help. Oral dosing of fluconazole 150 mg daily may speed resolution. Pseudomonas infection is treated with oral ciprofloxacin 500 mg b.i.d. for 10-14 days and topical tobramycin. Remind patients that this area has a poor blood supply, and resolution will not be quick. If there is no response to treatment after six weeks, refer the patient to dermatology to ensure accurate diagnosis. You may be treating the wrong pathogen or missing an underlying collagen vascular disease or traumatic picking.