Onychomycosis

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Onychomycosis
Classification and external resources
Toefungus.jpg
A toenail affected by onychomycosis
ICD-10 B35.1
ICD-9 110.1
DiseasesDB 13125
MedlinePlus 001330
eMedicine derm/300
MeSH D014009

Onychomycosis (also known as "dermatophytic onychomycosis,"[1] or "tinea unguium"[1]) means fungal infection of the nail.[2] It is the most common disease of the nails and constitutes about a half of all nail abnormalities.[3]

This condition may affect toenails or fingernails, but toenail infections are particularly common. It occurs in about 10% of the adult population.[4]

Signs and symptoms[edit]

Onychomycosis

The most common symptom of a fungal nail infection is the nail becoming thickened and discoloured: white, black, yellow or green. As the infection progresses the nail can become brittle, with pieces breaking off or coming away from the toe or finger completely. If left untreated, the skin can become inflamed and painful underneath and around the nail. There may also be white or yellow patches on the nailbed or scaly skin next to the nail,[5] and a foul smell.[6] There is usually no pain or other bodily symptoms, unless the disease is severe.[7] People with onychomycosis may experience significant psychosocial problems due to the appearance of the nail, particularly when fingers – which are always visible – rather than toenails are affected.[8]

Dermatophytids are fungus-free skin lesions that sometimes form as a result of a fungus infection in another part of the body. This could take the form of a rash or itch in an area of the body that is not infected with the fungus. Dermatophytids can be thought of as an allergic reaction to the fungus.

Causes[edit]

The causative pathogens of onychomycosis include dermatophytes, Candida, and nondermatophytic molds.[9] Dermatophytes are the fungi most commonly responsible for onychomycosis in the temperate western countries; while Candida and nondermatophytic molds are more frequently involved in the tropics and subtropics with a hot and humid climate.[10]

Dermatophytes[edit]

Trichophyton rubrum is the most common dermatophyte involved in onychomycosis. Other dermatophytes that may be involved are T. interdigitale, Epidermophyton floccosum, T. violaceum, Microsporum gypseum, T. tonsurans, T. soudanense A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale. The name T. mentagrophytes is now restricted to the agent of favus skin infection of the mouse; though this fungus may be transmitted from mice and their danders to humans, it generally infects skin and not nails.

Other[edit]

Other causative pathogens include Candida and nondermatophytic molds, in particular members of the mold generation Scytalidium (name recently changed to Neoscytalidium), Scopulariopsis, and Aspergillus. Candida spp. mainly cause fingernail onychomycosis in people whose hands are often submerged in water. Scytalidium mainly affects people in the tropics, though it persists if they later move to areas of temperate climate.

Other molds more commonly affect people older than 60 years, and their presence in the nail reflects a slight weakening in the nail's ability to defend itself against fungal invasion.

Risk factors[edit]

Aging is the most common risk factor for onychomycosis due to diminished blood circulation, longer exposure to fungi, and nails which grow more slowly and thicken, increasing susceptibility to infection. Nail fungus tends to affect men more often than women, and is associated with a family history of this infection.

Other risk factors include perspiring heavily, being in a humid or moist environment, psoriasis, wearing socks and shoes that hinder ventilation and do not absorb perspiration, going barefoot in damp public places such as swimming pools, gyms and shower rooms, having athlete's foot (tinea pedis), minor skin or nail injury, damaged nail, or other infection, and having diabetes, circulation problems, which may also lead to lower peripheral temperatures on hands and feet, or a weakened immune system.[11]

Diagnosis[edit]

To avoid misdiagnosis as nail psoriasis, lichen planus, contact dermatitis,nail bed tumors such as melanoma, trauma, or yellow nail syndrome, laboratory confirmation may be necessary.[9] The three main approaches are potassium hydroxide smear, culture and histology.[9] This involves microscopic examination and culture of nail scrapings or clippings. Recent results indicate the most sensitive diagnostic approaches are direct smear combined with histological examination,[12] and nail plate biopsy using periodic acid-Schiff stain.[13] To reliably identify nondermatophyte molds, several samples may be necessary.[14]

Classification[edit]

There are four classic types of onychomycosis:[15]

  • Distal subungual onychomycosis is the most common form of tinea unguium,[9] and is usually caused by Trichophyton rubrum, which invades the nail bed and the underside of the nail plate.
  • White superficial onychomycosis (WSO) is caused by fungal invasion of the superficial layers of the nail plate to form "white islands" on the plate. It accounts for only 10 percent of onychomycosis cases. In some cases, WSO is a misdiagnosis of "keratin granulations" which are not a fungus, but a reaction to nail polish that can cause the nails to have a chalky white appearance. A laboratory test should be performed to confirm.[16]
  • Proximal subungual onychomycosis is fungal penetration of the newly formed nail plate through the proximal nail fold. It is the least common form of tinea unguium in healthy people, but is found more commonly when the patient is immunocompromised.[9]
  • Candidal onychomycosis is Candida species invasion of the fingernails, usually occurring in persons who frequently immerse their hands in water. This normally requires the prior damage of the nail by infection or trauma.

Treatment[edit]

In approximately half of suspected nail fungus cases there is actually no fungal infection, but only nail deformity.[17] Because of this, a confirmation of fungal infection should precede treatment.[17] Avoiding use of oral antifungal therapy in persons without a confirmed infection is a particular concern because of the side effects of that treatment, and because persons without an infection should not have this therapy.[17]

Treatment of onychomycosis is challenging because the infection is embedded within the nail and is difficult to reach. It may take a year or more, since new nail growth must entirely replace old, infected growth.[18]

Medications[edit]

Most treatments are either topical or oral antifungal medications.[4] Oral medications include: terbinafine (76% effective), itraconazole (60% effective) and fluconazole (48% effective).[4] Oral terbinafine is better tolerated than itraconazole.[19] For superficial white onychomycosis, systemic rather than topical antifungal therapy is advised.[20]

Topical agents include: ciclopirox nail paint, clotrimazole, amorolfine or butenafine.[21] Topical treatments need to be applied daily for prolonged periods (at least 1 year).[22] Topical ciclopirox results in a cure in 6 to 9% and that amorolfine might be more effective.[4][22] Ciclopirox when used with terbinafine appears to be better than each agent alone.[4]

Heat[edit]

Research suggests that fungi are sensitive to heat, typically 40–60 °C. The basis of laser treatment is to try heat the nail bed to these temperatures in order to disrupt fungal growth.[23] There is ongoing research as of 2013 which looks promising.[4]

Other[edit]

Removing the affected part of the nail during treatment appears to improve outcomes.[4] Australian tea tree oil has failed to demonstrate benefit in the treatment of onychomycosis.[9]

Prognosis[edit]

Following effective treatment recurrence is common (10-50%).[4] Nail fungus can be painful and cause permanent damage to nails. It may lead to other serious infections if the immune system is suppressed due to medication, diabetes or other conditions. The risk is most serious for people with diabetes and with immune systems weakened by leukemia or AIDS, or medication after organ transplant. Diabetics have vascular and nerve impairment, and are at risk of cellulitis, a potentially serious bacterial infection; any relatively minor injury to feet, including a nail fungal infection, can lead to more serious complications.[24] Osteomyelitis (infection of the bone) is another, rare, possible complication.[5]

Epidemiology[edit]

A 2003 survey of diseases of the foot in 16 European countries found onychomycosis to be the most frequent fungal foot infection and estimates its prevalence at 27%.[25][26] Prevalence was observed to increase with age. In Canada, the prevalence was estimated to be 6.48%.[27] Onychomycosis affects approximately one-third of diabetics[28] and is 56% more frequent in people suffering from psoriasis.[29]

References[edit]

  1. ^ a b Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. p. 1135. ISBN 1-4160-2999-0. 
  2. ^ "onychomycosis" at Dorland's Medical Dictionary
  3. ^ Szepietowski JC, Salomon J (2007). "Do fungi play a role in psoriatic nails?". Mycoses 50 (6): 437–42. doi:10.1111/j.1439-0507.2007.01405.x. PMID 17944702. 
  4. ^ a b c d e f g h Westerberg, DP; Voyack, MJ (Dec 1, 2013). "Onychomycosis: current trends in diagnosis and treatment.". American family physician 88 (11): 762–70. PMID 24364524. 
  5. ^ a b NHS Choices: Symptoms of fungal nail infection
  6. ^ Mayo clinic: Nail fungus
  7. ^ Onychomycosis at eMedicine
  8. ^ Szepietowski JC, Reich A (September 2008). "Stigmatisation in onychomycosis patients: a population-based study". Mycoses 52 (4): 343–9. doi:10.1111/j.1439-0507.2008.01618.x. PMID 18793262. 
  9. ^ a b c d e f Westerberg D, Voyack MJ (December 2013). "Onychomycosis: Current Trends in Diagnosis and Management". Am Fam Physician (Review) 88 (11): 762–70. 
  10. ^ Chi CC, Wang SH, Chou MC (2005). "The causative pathogens of onychomycosis in southern Taiwan". Mycoses 48 (6): 413–20. doi:10.1111/j.1439-0507.2005.01152.x. PMID 16262878. 
  11. ^ Mayo Clinic – Nail fungus – risk factors
  12. ^ Karimzadegan-Nia M; Mir-Amin-Mohammadi A; Bouzari N, Firooz A (2007). "Comparison of direct smear, culture and histology for the diagnosis of onychomycosis". Australas. J. Dermatol. 48 (1): 18–21. doi:10.1111/j.1440-0960.2007.00320.x. PMID 17222296. 
  13. ^ Weinberg JM; Koestenblatt EK; Tutrone WD; Tishler HR; Najarian L (2003). "Comparison of diagnostic methods in the evaluation of onychomycosis". J. Am. Acad. Dermatol. 49 (2): 193–7. doi:10.1067/S0190-9622(03)01480-4. PMID 12894064. 
  14. ^ Shemer, A; Davidovici, B; Grunwald, MH; Trau, H; Amichai, B (2009). "New criteria for the laboratory diagnosis of nondermatophyte moulds in onychomycosis". The British journal of dermatology 160 (1): 37–9. doi:10.1111/j.1365-2133.2008.08805.x. PMID 18764841. 
  15. ^ James, William D.; Berger, Timothy G. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0. 
  16. ^ "AAPA". Cmecorner.com. Retrieved 2010-08-05. 
  17. ^ a b c American Academy of Dermatology (February 2013), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American Academy of Dermatology), retrieved 5 December 2013 , which cites
    • Roberts, D. T.; Taylor, W. D.; Boyle, J.; British Association of Dermatologists (2003). "Guidelines for treatment of onychomycosis". The British journal of dermatology 148 (3): 402–410. doi:10.1046/j.1365-2133.2003.05242.x. PMID 12653730. 
  18. ^ "Nail Fungus Treatment". Retrieved 2013-01-05. 
  19. ^ Haugh M, Helou S, Boissel JP, Cribier BJ (2002). "Terbinafine in fungal infections of the nails: a meta-analysis of randomized clinical trials". Br. J. Dermatol. 147 (1): 118–21. doi:10.1046/j.1365-2133.2002.04825.x. PMID 12100193. 
  20. ^ Baran R, Faergemann J, Hay RJ (2007). "Superficial white onychomycosis—a syndrome with different fungal causes and paths of infection". J. Am. Acad. Dermatol. 57 (5): 879–82. doi:10.1016/j.jaad.2007.05.026. PMID 17610995. 
  21. ^ Rodgers P, Bassler M (2001). "Treating onychomycosis". Am Fam Physician 63 (4): 663–72, 677–8. PMID 11237081. 
  22. ^ a b Crawford F, Hollis S (2007). "Topical treatments for fungal infections of the skin and nails of the foot". In Crawford, Fay. Cochrane Database Syst Rev (3): CD001434. doi:10.1002/14651858.CD001434.pub2. PMID 17636672. 
  23. ^ "Device-based Therapies for Onychomycosis Treatment". Retrieved 23 December 2012. 
  24. ^ Mayo clinic – Nail fungus: complications
  25. ^ Burzykowski, T.; Molenberghs, G.; Abeck, D.; Haneke, E.; Hay, R.; Katsambas, A.; Roseeuw, D.; Van De Kerkhof, P.; Van Aelst, R.; Marynissen, G. (2003). "High prevalence of foot diseases in Europe: Results of the Achilles Project". Mycoses 46 (11–12): 496–505. doi:10.1046/j.0933-7407.2003.00933.x. PMID 14641624.  edit
  26. ^ Verma S, Heffernan MP (2008). Superficial fungal infection: Dermatophytosis, onychomycosis, tinea nigra, piedra. In K Wolff et al., eds., Fitzpatrick's Dermatology in General Medicine, 7th ed., vol 2, pp. 1807–1821. New York: McGraw Hill.
  27. ^ Vender, R.; Lynde, C.; Poulin, Y. (2006). "Prevalence and epidemiology of onychomycosis". Journal of cutaneous medicine and surgery. 10 Suppl 2: S28–S33. PMID 17204229.  edit
  28. ^ Gupta, A.; Konnikov, N.; MacDonald, P.; Rich, P.; Rodger, N.; Edmonds, M.; McManus, R.; Summerbell, R. (1998). "Prevalence and epidemiology of toenail onychomycosis in diabetic subjects: A multicentre survey". The British journal of dermatology 139 (4): 665–671. PMID 9892911.  edit
  29. ^ Gupta, A.; Lynde, C.; Jain, H.; Sibbald, R.; Elewski, B.; Daniel Cr, 3.; Watteel, G.; Summerbell, R. (1997). "A higher prevalence of onychomycosis in psoriatics compared with non-psoriatics: A multicentre study". The British journal of dermatology 136 (5): 786–789. PMID 9205520.  edit