8/1/2017
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`\\\MERCK MANUAL
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`Professional Version
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`Professional / Dermatologic Disorders/ Nail Disorders
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`Onychomycosis
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`(Tinea Unguium)
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`By Chris G. Adigun, MD, Board-Certified
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`Dermatologist, Dermatology & Laser Center of
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`Chapel Hill
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`Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails
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`typically are deformed and discolored white or yellow. Diagnosis is by
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`appearance, wet mount, culture, PCR, or a combination. Treatment, when
`indicated, is with oral terbinafine or itraconazole.
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`(See also Overview of Nail Disorders.)
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`About 10% (range 2 to 14%) of the population has onychomycosis. Risk factors
`include
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`o Tinea pedis
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`- Preexisting nail dystrophy (eg, in patients with psoriasis)
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`0 Older age
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`0 Male sex
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`0 Exposure to someone with tinea pedis or onychomycosis (eg, a family
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`member or through public bathing)
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`0 Peripheral vascular disease or diabetes
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`-
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`Immunocompromise
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`Toenails are 10 times more commonly infected than fingernails. About 60 to 80%
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`of cases are caused by dermatophytes (eg, Trichophyton rubrum); dermatophyte
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`infection ofthe nails is called tinea unguium. Many of the remaining cases are
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`caused by nondermatophyte molds (eg, Aspergillus, Scopu/ariopsis, Fusarium).
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`Immunocompromised patients and those with chronic mucocutaneous
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`candidiasis may have candidal onychomycosis (which is more common on the
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`fingers). Subclinical onychomycosis can also occur in patients with recurrent tinea
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`pedis. Onychomycosis may predispose patients to lower extremity cellulitis.
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`Onychomycosis
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`Images provided by Thomas Habif, MD.
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`Onychomycosis of the Great Toes
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`Image courtesy of Dr. Edwin P. Ewing,Jr. via the Public Health Image Library of the
`Centers for Disease Control and Prevention.
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`Symptoms and Signs
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`Nails have asymptomatic patches of white or yellow discoloration and deformity.
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`There are 3 common characteristic patterns:
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`0 Distal subungual, in which the nails thicken and yellow, keratin and debris
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`accumulate distally and underneath, and the nail separates from the nail
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`bed (onycholysis)
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`- Proximal subungual, a form that starts proximally and is a marker of
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`immunosuppression
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`0 White superficial, in which a chalky white scale slowly spreads beneath the
`nail surface
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`Diagnosis
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`a Clinical evaluation
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`0 Potassium hydroxide wet mount examination
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`- Histopathologic examination of periodic acid-Schiff—stained nail clippings
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`and subungual debris
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`0 Culture
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`Onychomycosis is suspected by appearance; predictive clinical features include
`involvement of the 3rd or 5th toenail, involvement of the ist and 5th toenails on
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`the same foot, unilateral nail deformity, but only if the patient has tinea pedis.
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`Subclinical onychomycosis should be considered in patients with recurrent tinea
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`pedis.
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`Differentiation from psoriasis or lichen planus is important because the therapies
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`differ, so diagnosis is typically confirmed by microscopic examination and, unless
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`microscopic findings are conclusive, culture of scrapings or rarely PCR of
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`clippings. Scrapings are taken from the most proximal position that can be
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`accessed on the affected nail and are examined for hyphae on potassium
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`hydroxide wet mount and cultured. Histopathologic examination of periodic acid-
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`Schiff(PAS)—stained nail clippings and subungual debris may also be helpful.
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`Obtaining an adequate sample of nail for culture can be difficult because the
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`distal subungual debris, which is easy to sample, often does not contain living
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`fungus. Therefore, removing the distal portion of the nail with clippers before
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`sampling or using a small curette to reach more proximally beneath the nail
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`increases the yield. PCR can be done if cultures are negative and the cost of
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`finding a definitive diagnosis is warranted.
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`Treatment
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`0 Selective use of oral terbinafine or itraconazole
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`o Occasional use of topical treatments (eg, efinaconazole, tavaborole,
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`ciclopirox 8%, amorolfine)
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`Onychomycosis is not always treated because many cases are asymptomatic or
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`mild and unlikely to cause complications, and the oral drugs that are the most
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`effective treatments can potentially cause hepatotoxicity and serious drug
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`interactions. Some proposed indications for treatment include the following:
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`a Previous ipsilateral cellulitis
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`0 Diabetes or other risk factors for cellulitis
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`- Presence of bothersome symptoms
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`0 Psychosocial impact
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`0 Desire for cosmetic improvement (controversial)
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`Treatment is typically oral terbinafine or itraconazole. Terbinafine 250 mg
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`once/day for 12 wk (6 wk for fingernail) achieves a cure rate of 75 to 80% and
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`itraconazole 200 mg bid 1 wk/mo for 3 mo achieves a cure rate of 40 to 50%, but
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`the recurrence rate is estimated to be as high as 10 to 50%. It is not necessary to
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`treat until all abnormal nail is gone because these drugs remain bound to the nail
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`plate and continue to be effective after oral administration has ceased. The
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`affected nail will not revert to normal; however, newly growing nail will appear
`normal.
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`The newer topical agents efinaconazole and tavaborole can penetrate the nail
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`plate and are more effective than older topical agents (1—4).
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`Investigative treatments that have less frequent and/or less severe adverse
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`effects include laser therapy, new formulations of topical agents (including
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`efinaconazole), and new delivery systems for terbinafine (5,6). Topical antifungal
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`nail lacquer containing ciclopirox 8% or amorolfine 5% (not available in the US) is
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`occasionally effective as primary treatment (cure rate of about 30%) and can
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`improve cure rate when used as an adjunct with oral drugs, particularly in
`resistant infections.
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`To limit relapse, the patient should trim nails short, dry feet after bathing, wear
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`absorbent socks, and use antifungal foot powder. Old shoes may harbor a high
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`density of spores and, if possible, should not be worn.
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`Treatment references
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`http://www.merckmanuals.com/professional/dermatologic—disorders/naiI-disorders/onychomycosis
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`Elewski BE, Tosti A: Tavaborole for the treatment of onychomycosis. Expert
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`Opin Pharmacother 15(10):1439-1448, 2014. doi:
`10.1517/14656566.2014.921158
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`Gupta AK, Daigle D: Tavaborole (AN-2690) for the treatment of
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`onychomycosis of the toenail in adults. Expert Rev Anti Infect Ther
`12(7):735-742, 2014. doi: 10.1586/14787210.2014.915738.
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`Elewski BE, Rich P, Pollak R, et al: Efinaconazole 10% solution in the
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`treatment of toenail onychomycosis: Two phase III multicenter, randomized,
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`double-blind studies] Am Acad Dermatol 68(4):600-608, 2013. doi:
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`10.1016/j.jaad.2012.10.013.
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`Jo Siu WJ, Tatsumi Y, Senda H, et al: Comparison of in vitro antifungal
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`activities of efinaconazole and currently available antifungal agents against
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`a variety of pathogenic fungi associated with onychomycosis. Antimicrob
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`Agents Chemother 57(4):1610-1616, 2013. doi: 10.1128/AAC.02056-12.
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`Adigun CG, Vlahovic TC, McClellan MB, et al:Efinaconazole10% and
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`tavaborole 5% penetrate across poly-ureaurethane 16%: Results of in vitro
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`release testing and clinical implications of onychodystrophy in
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`onychomycosis.] Drugs Dermatol 1;15(9):1116-1120, 2016.
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`Baker 5], Zhang YK, Akama T, et al: Discovery of a new boron-containing
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`antifungal agent, 5-fluoro-1,3-dihydro-1-hydroxy-2,1- benzoxaborole
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`(AN2690), for the potential treatment of onychomycosis.] Med Chem
`27;49(15):4447-4450, 2006.
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`Key Points
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`Onychomycosis - Dermatologic Disorders - Merck Manuals Professional Edition
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`- Onychomycosis is highly prevalent, particularly among older men and
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`patients with compromised distal circulation, nail dystrophies, and/or tinea
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`pedis.
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`0 Suspect the diagnosis based on appearance and the pattern of nail
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`involvement and confirm it by microscopy and sometimes culture or PCR.
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`0 Treatment is warranted only if onychomycosis causes complications or
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`troublesome symptoms.
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`0
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`If treatment is warranted, consider terbinafine (the most effective
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`treatment) and measures to prevent recurrence (eg, limiting
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`moisture,discarding old shoes, trimming nails short).
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`Last full review/revision February 2017 by Chris G. Adigun, MD
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`6 MERCK
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`© 2017 Merck Sharp & Dohme Corp, a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA
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