eMedicine Specialties > Dermatology > Nails

Onychomycosis

Antonella Tosti, MD, Professor, Department of Dermatology, Director, Center of Allergology at the Institute of Clinical Dermatology, S Orsola Hospital, University of Bologna, Italy

Updated: Aug 17, 2009

Introduction

Background

Onychomycosis (OM) refers to a fungal infection that affects the toenails or the fingernails. Onychomycosis may involve any component of the nail unit, including the nail matrix, nail bed, or nail plate. Onychomycosis is not life threatening, but it can cause pain, discomfort, and disfigurement and may produce serious physical and occupational limitations. Psychosocial and emotional effects resulting from onychomycosis are widespread and may have a significant impact on quality of life.¹

The main subtypes of onychomycosis are distal lateral subungual onychomycosis (DLSO), white superficial onychomycosis (WSO), proximal subungual onychomycosis (PSO), endonyx onychomycosis (EO), and candidal onychomycosis. Patients may have a combination of these subtypes. Total dystrophic onychomycosis refers to the most advanced form of any subtype.

Pathophysiology

The pathogenesis of onychomycosis depends on the clinical subtype. In distal lateral subungual onychomycosis, the most common form of onychomycosis, the fungus spreads from plantar skin and invades the nail bed via the hyponychium. Inflammation occurring in these areas of the nail apparatus causes the typical physical signs of distal lateral subungual onychomycosis. In contrast, white superficial onychomycosis is a rarer presentation caused by direct invasion of the surface of the nail plate. In proximal subungual onychomycosis, the least common subtype, fungi penetrate the nail matrix via the proximal nail fold and colonize the deep portion of proximal nail plate. Endonyx onychomycosis is a variant of distal lateral subungual onychomycosis in which the fungi infect the nail via the skin and directly invade the nail plate. Total dystrophic onychomycosis involves the entire nail unit (see Media file 1).

Distal subungual onychomycosis. Onycholysis and yellow streak.

Nail invasion by Candida is not common because the yeast needs an altered immune response as a predisposing factor to be able to penetrate the nails. Despite the frequent isolation of Candida from the proximal nail fold or the subungual space of patients with chronic paronychia or onycholysis, in these patients Candida is only a secondary colonizer. In chronic mucocutaneous candidiasis, the yeast infects the nail plate and eventually the proximal and lateral nail folds.

Frequency

United States

The recent proliferation of fungal infections in the United States can be traced to the large immigration of dermatophytes, especially Trichophyton rubrum, from West Africa and Southeast Asia to North America and Europe.²

International

The incidence of onychomycosis has been reported to be 2-13% in North America.³ A multicenter survey in Canada showed the prevalence of onychomycosis at 6.5%.⁴ Onychomycosis accounts for half of all nail disorders, and onychomycosis is the most common nail disease in adults. Toenails are much more likely to be infected than fingernails. Thirty percent of patients with a cutaneous fungal infection also have onychomycosis. The incidence of onychomycosis has been increasing, owing to such factors as diabetes, immunosuppression, and increasing age.²

Studies in the United Kingdom, Spain, and Finland found prevalence rates of onychomycosis to be 3-8%.

Race

Onychomycosis affects persons of all races.

Sex

Onychomycosis affects males more commonly than females. However, candidal infections are more common in women than in men.

Age

Studies indicate that adults are 30 times more likely to have onychomycosis than children. Onychomycosis has been reported to occur in 2.6% of children younger than 18 years but as many as 90% of elderly people.

Clinical

History

Onychomycosis is usually asymptomatic; therefore, patients usually first present for cosmetic reasons without any physical complaints.

• As the disease progresses, onychomycosis may interfere with standing, walking, and exercising.
• Patients may report paresthesia, pain, discomfort, and loss of dexterity. They also may report loss of self-esteem and lack of social interaction.
• A careful history may reveal many environmental and occupational risk factors.

Physical

The subtypes of onychomycosis may be distinguished on the basis of their usual presenting clinical features.

• In distal lateral subungual onychomycosis, the nail shows subungual hyperkeratosis and onycholysis, which is usually yellow-white in color. Yellow streaks and/or yellow onycholytic areas in the central portion of the nail plate are commonly observed.

Distal subungual onychomycosis. Onycholysis and yellow streak.

Distal subungual onychomycosis. Subungual hyperkeratosis onycholysis and yellow streak.

• Endonyx onychomycosis presents as a milky white discoloration of the nail plate, but, in contrast to distal lateral subungual onychomycosis, no evidence of subungual hyperkeratosis or onycholysis is present.
• White superficial onychomycosis is confined to the toenails and manifests as small, white, speckled or powdery patches on the surface of the nail plate. The nail becomes roughened and crumbles easily. Molds produce a deep variety of white superficial onychomycosis characterized by a larger and deeper nail plate invasion.

White superficial onychomycosis.

• Proximal subungual onychomycosis presents as an area of leukonychia in the proximal nail plate that moves distally with nail growth,. In proximal subungual onychomycosis caused by molds, leukonychia is typically associated with marked periungual inflammation.

Proximal subungual onychomycosis. Proximal leukonychia.

• Total dystrophic onychomycosis presents as a thickened, opaque, and yellow-brown nail.
• In Candida onychomycosis associated with chronic mucocutaneous candidiasis or immunodepression, several or all digits are affected by total onychomycosis associated with periungual inflammation. The digits often take on a bulbous or drumstick appearance.

Candidal onychomycosis in a patient with chronic mucocutaneous candidiasis. Total onychomycosis and paronychia.

Causes

Onychomycosis is caused by 3 main classes of fungi: dermatophytes, yeasts, and nondermatophyte molds. Dermatophytes are by far the most common cause of onychomycosis. Two major pathogens are responsible for approximately 90% of all onychomycosis cases. T rubrum accounts for 70% and Trichophyton mentagrophytes accounts for 20% of all cases. Onychomycosis caused by nondermatophyte molds (Fusarium species, Scopulariopsis brevicaulis, Aspergillus species) is becoming more common worldwide, accounting for up to 15% of cases in some countries. Onychomycosis due to Candida is rare.⁵

• T rubrum is the most common pathogen in distal lateral subungual onychomycosis.
• Proximal subungual onychomycosis due to T rubrum infection is typical of immunosuppressed patients . Additionally, Proximal subungual onychomycosis with periungual inflammation is usually caused by molds
• White superficial onychomycosis is usually caused by T mentagrophytes; nondermatophyte molds cause deep white superficial onychomycosis.
• Candida albicans nail infection is observed in premature children, in immunocompromised patients, and in persons with chronic mucocutaneous candidiasis.

Risk factors for onychomycosis include family history, increasing age, poor health, prior trauma, warm climate, participation in fitness activities, immunosuppression (eg, HIV, drug induced), communal bathing, and occlusive footwear.

Differential Diagnoses

Contact Dermatitis, Irritant
Lichen Planus
Malignant Melanoma
Psoriasis, Nails

Other Problems to Be Considered

Bacterial paronychia (including pseudomonal infection) 
Darier disease
Drug reaction (eg, tetracyclines, quinolones, psoralens) 
Pachyonychia congenita
Periodic nail shedding
Thyroid disease
Yellow nail syndrome 
Melanonychia (caused by malignant melanoma)

Workup

Laboratory Studies

The clinical features of onychomycosis may mimic a large number of other nail disorders. Therefore, laboratory diagnosis of onychomycosis must be confirmed before beginning a treatment regimen.

• Direct microscopy
  • A 20% potassium hydroxide (KOH) preparation in dimethyl sulfoxide (DMSO) is a useful screening test to rule out the presence of fungi. Before obtaining a specimen, the nails must be clipped and cleansed with an alcohol swab to remove bacteria and debris. The preparation does not require heating or prolonged incubation if DMSO is a component of the KOH solution.
  • In distal lateral subungual onychomycosis, a specimen should be obtained from the nail bed by curettage. The onycholytic nail plate should be removed and the sample should be obtained at a site most proximal to the cuticle, where the concentration of hyphae is greatest.
  • In proximal subungual onychomycosis, the overlying nail plate must initially be pared with a No. 15 blade. Then, a sample of the ventral nail plate may be taken. A No. 15 blade may also be used to remove a specimen from the nail surface in white superficial onychomycosis.
  • Specimens suspected of candidal onychomycosis should be taken from the affected nail bed closest to the proximal and lateral edges.
  • Nail fragments must be small enough for examination under low power. Large pieces of nail plate may be pulverized prior to microscopy by using a hammer or a nail micronizer. Counterstains, such as chlorazol black E or Parker blue-black ink, may be used to accentuate the hyphae.
  • Shemer et al reported that drilling to obtain specimens and taking the sample from a more proximal site yield better results.⁶
• Culture
  • Direct microscopy cannot identify the specific pathogen involved in onychomycosis. A fungal culture must be used to identify the species of organism.⁷ Nondermatophyte molds may be resistant to the conventional therapy used for the more common dermatophytes.⁸ Therefore, 2 types of growth medium should be used, one with cycloheximide (dermatophyte test medium [DTM], Mycosel, or Mycobiotic) to select for dermatophytes and one without cycloheximide (Sabouraud glucose agar, Littman oxgall medium, or inhibitory mold agar) to isolate yeasts and nondermatophyte molds.⁹
  • Cultures should be obtained from pulverized nail scrapings or clippings while the patient has abstained from antifungal medication for at least 2 weeks. The specimen should be kept at room temperature with the cap placed loosely over the inoculated medium.

A negative mycological result does not rule out onychomycosis, because direct microscopy may be negative in up to 10% of cases and culture in up to 30% of cases

Other Tests

Polymerase chain reaction (PCR) assays have been developed to detect T rubrum DNA from infected nails.¹⁰

Histologic Findings

Histologic examination of the nail is a very useful alternative to culture or KOH testing. Nail clippings may be sent to the laboratory for diagnosis in a formalin-filled container, or, as a last resort, an incisional nail biopsy (by punch or scalpel) may be performed to help confirm the diagnosis. Staining in the laboratory should be performed with periodic acid-Schiff stain (PAS) or methenamine silver stain to reveal fungal elements. A comparison of diagnostic methods revealed that a nail biopsy and staining with PAS is the most sensitive technique available to diagnose onychomycosis.¹¹ Examining formalin-fixed, PAS-stained specimens has a higher probability (a higher negative predictive value) than KOH examination in determining that a patient is disease free if the test results are negative.

In addition to excluding other conditions (eg, psoriasis, lichen planus), the topographic distribution, the density, and the nature of the fungal elements may help guide treatment. Biopsy specimens of onychomycosis may show features of psoriasiform hyperplasia, including parakeratosis, thinned rete ridges, narrow suprapapillary plates, and dilated tortuous capillaries. As in direct microscopy, histopathologic diagnosis does not identify the species of causative pathogen.

Treatment

Medical Care

Treatment of onychomycosis depends on the clinical type of the onychomycosis, the number of affected nails, and the severity of nail involvement. A systemic treatment is always required in proximal subungual onychomycosis and in distal lateral subungual onychomycosis involving the lunula region. White superficial onychomycosis and distal lateral subungual onychomycosis limited to the distal nail can be treated with a topical agent. A combination of systemic and topical treatment increases the cure rate. Because the rate of recurrence remains high, even with newer agents, the decision to treat should be made with a clear understanding of the cost and risks involved, as well as the risk of recurrence.

• Topical antifungals
  • The use of topical agents should be limited to cases involving less than half of the distal nail plate or for patients unable to tolerate systemic treatment. Agents include amorolfine (approved in other countries), ciclopirox olamine 8% nail lacquer solution, and bifonazole/urea (available outside the United States).
  • Topical treatments alone are generally unable to cure onychomycosis because of insufficient nail plate penetration. Ciclopirox and amorolfine solutions have been reported to penetrate through all nail layers but have low efficacy when used as monotherapy.¹² They may be useful as adjunctive therapy in combination with oral therapy or as prophylaxis to prevent recurrence in patients cured with systemic agents.
• Oral therapy^13,14,15
  • The newer generation of oral antifungal agents (itraconazole and terbinafine) has replaced older therapies in the treatment of onychomycosis. They offer shorter treatment regimens, higher cure rates, and fewer adverse effects. Fluconazole (not approved by the US Food and Drug Administration [FDA] for treatment of onychomycosis) offers an alternative to itraconazole and terbinafine. Derivatives of fluconazole may also be available soon. The efficacy of the newer antifungal agents lies in their ability to penetrate the nail plate within days of starting therapy. Evidence shows better efficacy with terbinafine than with other oral agents (see Prognosis).¹⁶
  • To decrease the adverse effects and duration of oral therapy, topical treatments and nail avulsion may be combined with oral antifungal management.¹⁷

Surgical Care

Surgical approaches to onychomycosis treatment include mechanical, chemical, or surgical nail avulsion.

• Chemical removal by using a 40-50% urea compound is painless and useful in patients with very thick nails
• Removal of the nail plate should be considered an adjunctive treatment in patients undergoing oral therapy.
• A combination of oral, topical, and surgical therapy can increase efficacy and reduce cost.

Activity

Activity does not need to be limited during treatment, but patients should be educated about avoiding direct contact with high-risk areas in public places.

Medication

The goals of pharmacotherapy for onychomycosis are to reduce morbidity and to prevent complications.

Antifungals

The goals of pharmacotherapy for onychomycosis are to reduce morbidity and to prevent complications.^18,19

Terbinafine (Lamisil)

Inhibits squalene epoxidase, which decreases ergosterol synthesis, causing fungal cell death. Use medication until symptoms significantly improve. More studies needed to establish efficacy of pulse regimens and optimal duration of treatment.

Dosing

Adult

Toenails: 250 mg PO qd for 12 wk
Fingernails: 250 mg PO qd for 6 wk
Pulse therapy: 500 mg PO qd for 1 wk/mo for 4 mo (toenails) or 2 mo (fingernails); 250 mg qd for 1 wk q3mo for 4 cycles has also been used

Pediatric

Weight-based dosing
12-20 kg: 62.5 mg/d PO
20-40 kg: 125 mg/d PO
>40 kg: 250 mg/d PO
Treatment duration as in adults

Interactions

May decrease cyclosporine effects; toxicity may increase with rifampin and cimetidine

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Discontinue use if chemical irritation develops with topical use; if hepatobiliary dysfunction, neutropenia, Stevens-Johnson syndrome, or changes in ocular lens or retina develop, discontinue use

Itraconazole (Sporanox)

Fungistatic activity. Synthetic triazole antifungal agent that slows fungal cell growth by inhibiting CYP-450–dependent synthesis of ergosterol, a vital component of fungal cell membranes.

Dosing

Adult

Toenails: 200 mg PO qd for 12 wk or 200 mg PO bid for 1 wk, then 3 wk without treatment; repeat for 3 pulses
Fingernails: 200 mg PO bid for 1 wk, then 3 wk without treatment, then 200 mg PO bid for 1 additional wk for 2 pulses

Pediatric

Not established; suggested dose of 100 mg/d for systemic fungal infections

Interactions

Antacids may reduce absorption; edema may occur with coadministration of calcium channel blockers (eg, amlodipine, nifedipine); hypoglycemia may occur with sulfonylureas; may increase tacrolimus and cyclosporine plasma concentrations when high doses are used; rhabdomyolysis may occur with coadministration of HMG-CoA reductase inhibitors (eg, lovastatin, simvastatin); coadministration with cisapride can cause cardiac rhythm abnormalities and death; may increase digoxin levels; coadministration may increase plasma levels of midazolam or triazolam; phenytoin and rifampin may reduce itraconazole levels (phenytoin metabolism may be altered)

Contraindications

Documented hypersensitivity; coadministration with cisapride may cause adverse cardiovascular effects (possibly death); heart failure has been reported

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Hepatic disease; achlorhydria (may impair absorption); not recommended in breastfeeding; heart failure has been reported

Fluconazole (Diflucan)

Fungistatic activity. Synthetic oral antifungal (broad-spectrum bistriazole) that selectively inhibits fungal CYP-450 and sterol C-14 alpha-demethylation, which prevents conversion of lanosterol to ergosterol, thereby disrupting cellular membranes. Treatment should continue until infection resolves.

Dosing

Adult

Toenails: 150-300 mg PO qwk
Fingernails: 150-300 mg PO qwk

Pediatric

3-6 mg/kg PO qd for 14-28 d or 6-12 mg/kg PO qd, depending on severity of infection

Interactions

Levels may increase with thiazides; levels may decrease with chronic coadministration of rifampin; coadministration may decrease phenytoin clearance; may increase concentrations of theophylline, tolbutamide, glyburide, and glipizide; effects of anticoagulants may increase with coadministration; increases in cyclosporine concentrations may occur when administered concurrently

Contraindications

Documented hypersensitivity; concomitant warfarin, theophylline, oral hypoglycemics, phenytoin, cyclosporine, rifampin, hydrochlorothiazide, cimetidine, or cisapride

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Monitor closely if rashes develop and discontinue drug if lesions progress; may cause clinical hepatitis, cholestasis, and fulminant hepatic failure (including death), with underlying medical conditions (eg, AIDS, malignancy) and while taking multiple concomitant medications; not recommended in breastfeeding

Ciclopirox (Penlac)

Interferes with synthesis of DNA, RNA, and protein by inhibiting transport of essential elements in fungal cells.

Dosing

Adult

Apply evenly over entire nail plate and 5 mm of surrounding skin qhs or 8h before washing; if possible, apply to nail bed, hyponychium, and undersurface of nail plate when free of nail bed; do not remove product on daily basis; apply daily over previous coat and remove with alcohol q7d; repeat cycle throughout duration of therapy

Pediatric

Not established

Interactions

None reported

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Avoid contact with eyes and other internal routes

Follow-up

Further Outpatient Care

• Although hepatotoxic reactions are unlikely, periodic monitoring of patients undergoing oral antifungal therapy should include a CBC count and measurements of liver enzyme levels approximately every 4-6 weeks.
• Treatment may be discontinued after standard dosing with terbinafine or itraconazole when no evidence of fungal infection (by microscopy or culture) is present. Nails may continue to look dystrophic after a cure is achieved in the laboratory.
• After antifungal therapy, disease-free nail growth should be measured at every visit. Nails should grow at a rate of 1.5-2 mm per month and may take up to 1 year to look normal. A clinician may consider an additional dose of antifungal medication if the outgrowth distance slows or stops after discontinuing therapy.

Complications

• Skin injury adjacent to the nail may allow organisms to colonize, thereby increasing the risk of infectious complications. Reports of complications in elderly persons and persons with diabetes include cellulitis, osteomyelitis, sepsis, and tissue necrosis.

Prognosis

• The goals for antifungal therapy are mycological cure and a normal looking nail. Mycological cure can be evaluated at the end of treatment, while clinical cure requires several more months owing to slow nail growth.²⁰
• Clinical trials have repeatedly demonstrated higher efficacy for terbinafine compared with other antifungal treatments.^16,21
• A meta-analysis of 18 studies on terbinafine, 6 studies on pulse itraconazole, and 3 studies on fluconazole for onychomycosis showed a mycological cure rate of 76%, 63 %, and 48 % respectively.²²
• Yellow streaks along the lateral margin of the nail and/or presence of yellow onycholytic areas in the central portion of the nail (dermatophytoma) are associated with a poor response to treatment.
• Residual nail changes persist in most patients as a result of the frequent association of onychomycosis with traumatic toenail dystrophies.
• Onychomycosis caused by molds, particularly Fusarium species, are often not responsive to systemic therapy.
• Recurrence (relapse or reinfection) of onychomycosis is not uncommon, with reported rates ranging from 10-53%.
• Fungal infections of the fingernails have a much more favorable prognosis than toenail infections.

Patient Education

• Patients should be educated about the use of appropriate footwear, especially in high-exposure areas such as communal bathing facilities and health clubs.
• Following treatment, patients must be advised that nails may not appear normal for up to 1 year, and prophylactic antifungal therapy may be required to prevent reinfection of the skin and the nails. Patients may use topical terbinafine cream twice daily for 1-2 weeks for early tinea pedis or a 1-week pulse of itraconazole (200 mg PO bid) at the first signs of onychomycosis.¹⁹
• For excellent patient education resources, visit eMedicine's Psoriasis Center and Yeast and Fungal Infections Center. Also, see eMedicine's patient education articles Nail Psoriasis and Onychomycosis.

Miscellaneous

Special Concerns

• HIV disease: Onychomycosis in patients who are immunocompromised is associated with increased severity and morbidity. Lesions may appear atypical and require more aggressive management compared with the healthy population. Proximal subungual (ie, proximal subungual onychomycosis) involvement is much more prevalent in patients with HIV infection than in those without HIV infection. In this population, white superficial onychomycosis is more commonly caused by T rubrum, rather than T mentagrophytes.
• Diabetes²³ : The diabetic foot may lead to serious complications associated with onychomycosis. Peripheral neuropathy and sensory loss may lead to increased trauma without pain in patients with diabetes. Bacterial colonization and vascular insufficiency may exacerbate the problem and may lead to serious sequelae. A clinical guideline summary from the American College of Foot and Ankle Surgeons, Diabetic foot disorders: a clinical practice guideline, may be helpful.²⁴
• Elderly age²⁵ : Onychomycosis in elderly people is complicated by diseases (eg, poor vision, arthritis) that prevent optimal foot care. Nail changes are much more common in elderly persons and often involve the fingernails and the toenails. The potential for drug-drug interactions is more evident and must be addressed before initiating oral therapy.

Multimedia

Media file 1: Distal subungual onychomycosis. Onycholysis and yellow streak.

Media file 2: Distal subungual onychomycosis. Subungual hyperkeratosis onycholysis and yellow streak.

Media file 3: Proximal subungual onychomycosis. Proximal leukonychia.

Media file 4: White superficial onychomycosis.

Media file 5: Candidal onychomycosis in a patient with chronic mucocutaneous candidiasis. Total onychomycosis and paronychia.

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Keywords

onychomycosis, white superficial onychomycosis, distal lateral subungual onychomycosis, proximal subungual onychomycosis, endonyx onychomycosis, candidal onychomycosis, mold onychomycosis, total dystrophic onychomycosis, OM, unguium, fungal infection of the toenail, fungal infection of the fingernail, DLSO, WSO, PSO, EO

Contributor Information and Disclosures

Author

Antonella Tosti, MD, Professor, Department of Dermatology, Director, Center of Allergology at the Institute of Clinical Dermatology, S Orsola Hospital, University of Bologna, Italy
Antonella Tosti, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

Medical Editor

Richard K Scher, MD, Professor of Dermatology, University of North Carolina
Richard K Scher, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Cryosurgery, American College of Physicians, American Dermatological Association, American Geriatrics Society, American Medical Association, Association of Military Surgeons of the US, International Society for Dermatologic Surgery, New York Academy of Sciences, Noah Worcester Dermatological Society, Rhode Island Medical Society, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

Pharmacy Editor

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Jeffrey Meffert, MD, Assistant Clinical Professor of Dermatology, University of Texas Health Science Center-San Antonio
Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society
Disclosure: Nothing to disclose.

CME Editor

Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University
Catherine Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors, Mark Blumberg, MD, MS, Gary R. Kantor, MD, and John Ratz, MD, MBA, to the development and writing of this article.

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