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Fungal Nail Infections: Onychomycosis

General | January 17, 2015 | Author: The Super Pharmacist

general

Fungal Nail Infections: Onychomycosis

Fungal nail infections are common, causing a thickening and poor cosmetic appearance of the nail which can sometimes become painful. It more commonly affects toenails (>80%) than fingernails, and is more prevalent in people aged over 55 and young people who regularly share communal showers (1). A number of studies show global prevalence rates ranging from 3-26% worldwide, with infections found most frequently in countries with warmer climates (2). As the incidence of fungal nail infections is closely related to other factors such as diabetes mellitus, increasing rates of immunosuppression and a population that is getting older, it is predicted that the number of cases globally will continue to increase (3).

Diagnosing fungal infections

How can someone be certain that the condition is fungal? What are the diagnostic tools?

The large majority of fungal nail infections (>90%) are caused by dermatophyte fungi (4), although they can also occasionally be caused by other types of fungi such as Candida. Fungal nail infections can often be mistaken for other ailments: a quick diagnostic test, where a clipping of the nail will be sent to a laboratory, provides further information on the exact cause of the infection (and rules out any other conditions in the process).

Diagnosing fungal infectionsMost commonly, nail clippings are sent for microscopy. As there is a high false-positive rate in this testing method (fungal organisms can exist within the nail naturally, rather than as an invasive infection), culture testing is also used because it has increased sensitivity and can determine particular species of fungi. However, this process requires a longer period of time (often between 4-6 weeks for accurate results) than microscopy, where results are typically available within 2-3 days.

What else might an abnormal nail be?

Approximately 50% of nail samples that are sent for laboratory testing confirm a fungal infection. There are a wide number of other causes that produce similar symptoms. These include:

  • Systemic disease, such as thyroid disease, peripheral vascular disease or diabetes
  • Eczema
  • Poor foot care (including ill-fitting shoes)
  • Psoriatic nail disease
  • Rarer systemic disorders such as yellow nail syndrome, nail-patella syndrome and Darier’s disease
  • Lichen planus (an infection that causes the skin to develop an itchy rash)

Occasionally, laboratory testing of the toenail will also reveal idiosyncratic drug reaction to tetracyclines, psoralens and quinolones. If this is the case, your doctor will make a decision on the best course of treatment to ensure topical antibiotics that may cause harm are avoided. The wide range of additional medical problems that can affect the toenail are a reminder of the importance of laboratory testing for an accurate diagnosis: the misdiagnosis of fungal nail infection can affect the efficacy of prescribed treatment.

Treatments available for confirmed onychomycosis

Fungal nail infections can be treated and cured, although the course of medicine is often long and some treatments can take a number of months before they begin to be effective.

Traditionally, there has been a reluctance to treat fungal nail infections as it was considered to be a trivial, largely cosmetic, problem.

However, it is now considered that without treatment there is a sufficient risk that the condition can spread to other toenails and create conditions in which recurrent bacterial infections can occur. 

There is also a public health argument regarding increased treatment, focusing on the need to lessen the reservoir of fungi in communal areas (such as swimming baths) where its spread is common.

Antifungal medicines, in the form of tablets or nail paint, are the two most common treatment options. Terbinafine and itraconazole are the two most commonly prescribed medicines for fungal infections. Less commonly, fluconazole and griseofulvin are also used to treat the condition. Oral medications are taken for an average of three months for toenail infections, and topical treatments may need to be applied for up to 12 months, or until complete eradication of the infection.

What are the success rates of these treatments?

There is no medical necessity to treat fungal nail infection, so the use of various treatment options often involves balancing the probability of their success with some of the known side effects associated with their use. Even after a successful course of treatment there is no guarantee that the affected nail will look completely normal, and a relapse of fungal nail infection will usually occur in around 20-25% of people (5).

Diagnosing fungal infectionsTopical therapies that are applied directly to the affected area have been evidenced to be more effective than placebo, although their efficacy and impact is often compromised by poor application or penetration in the affected nail plate area (6).

There is no evidence for their use in conjunction with oral antifungal treatment and it is not recommended (7).

Systemic therapies, often recommended as first line treatment for the large majority of people with fungal nail infections, are done so due to their greater effectiveness.

Terbinafine is the primary recommended treatment as comparative studies have shown it to be more effective than itraconazole. A systematic review of 122 available studies, comparing treatment in over 20,000 patients, found it to be more efficacious and have a higher cure rate(8).  However, there are some limitations and side effects associated with its use: It is not licensed for use in children, and some incidents of severe skin and hepatotoxic reactions have been reported following its use.

Itraconazole is the preferred first line treatment for the treatment of fungal nail infections that are caused by Candida fungi (which account for approximately 8% of all cases). It can also cause hepatotoxicity and is not for use in children. Additionally, it is not recommended for use in pregnant women. The course of treatment time, along with terbinafine, tends to be around three months. On the other hand, griseofulvin requires a longer treatment period of at least six months. It also has low cure and high relapse rates, and as such is now a rarely used treatment option (9).

Some preliminary studies have espoused the benefits of laser treatment as a longer term effective cure of fungal nail infection, although this statement is often based on a limited number of studies with low levels of participants. Further randomised controlled trials, covering larger populations, are required to evaluate their long-term success to see if they have a role to play as a possible future treatment option (10).

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References

1. Ginarte M, Garcia-Doval I, Monteguado B, Cabinallas M. et al. (2009). Observer agreement in toenail disorders: implications for diagnosis and clinical research. Br J Dermatol 160(6):1315-7

2. Szepietowski JC, Reich A. (2008). Stigmatisation in onychomycosis patients: a population-based study. Mycoses.

3. Gulcan A, Gulcan E, Oksuz S, Sahin I, Kaya D. (2011). Prevalence of toenail onychomycosis in patients with type 2 diabetes mellitus and evaluation of risk factors. J Am Podiatr Med Assoc 101(1):49-54

4. Gupta AK, Cooper EA, Paquet M. (2013). Recurrences of dermatophyte toenail onychomycosis during long-term follow-up after successful treatments with mono- and combined therapy of terbinafine and itraconazole. J Cutan Med Surg 17(3):201-6

5. Gupta AK, Simpson FC. (2012). New therapeutic options for onychomycosis. Expert Opin Pharmacother. 13(8):1131-42

5. Shivakumar HN, Juluri A, Desai BG, Murthy SN. (2012). Ungual and Transungual drug delivery. Drug Dev Ind Pharm 38(8):901-11

6. National Institute of Care Excellence (NICE) Clinical Knowledge Summaries (CKS): Fungal nail infection management. Available online at http://cks.nice.org.uk/fungal-nail-infection

7. Chang CH, Young-Xu Y, Kurth T et al. (2007). The safety of oral antifungal treatments for superficial dermatophytosis and onychomycosis: a meta-analysis. Am J Med 120(9):791-8

8. Loo DS. (2006). Systemic antifungal agents: an update of established and new therapies. Adv Dermatol 22:101-24

9. Kimura U, Takeuchi K, Kinoshita A, Takamori K, Hiruma M, Suga Y. (2012). Treating onychomycoses of the toenail: clinical efficacy of the sub-millisecond 1,064 nm Nd: YAG laser using a 5 mm spot diameter. J Drugs Dermatol

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