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Non-dermatophyte mould onychomycosis

Author: Richa Tripathi, Consultant Dermatologist, Grande International Hospital, Kathmandu, Nepal. Copy edited by Gus Mitchell. November 2021


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Non-dermatophyte mould onychomycosis — codes and concepts
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What is non-dermatophyte mould onychomycosis?

Non-dermatophyte mould onychomycosis (NDMO) is an opportunistic fungal nail infection (onychomycosis) caused by moulds.

Moulds are ubiquitous in the environment, and thus are common contaminants that grow in nail fungal culture. Most moulds are non-keratolytic (except for Neoscytalidium dimidiatum) and require the presence of underlying trauma or other nail disease to penetrate the nail.

Mould infections

Who gets non-dermatophyte mould onychomycosis?

Non-dermatophyte mould onychomycosis constitutes approximately 10% of onychomycosis cases globally. Recent reports suggest a rise in prevalence, especially cases presenting with a dermatophyte co-infection.

Risk factors identified for NDMO are similar to those for onychomycosis as a whole.

Risk factors include:

  • Climate: hot and humid
  • Occupational exposures: gardening, farming
  • Occlusive footwear
  • Co-morbid conditions:           
    • Diabetes
    • Peripheral vascular disease
    • Immunosuppression
    • Chronic dermatologic conditions such as psoriasis
  • Hyperhidrosis
  • Local nail trauma.

What causes non-dermatophyte mould onychomycosis?

Different moulds have been identified as causing onychomycosis based on the geographical region. The most common species reported are:

  • Aspergillus sp.
  • Scopulariopsis sp.
  • Neoscytalidium sp.
  • Acremonium sp.
  • Fusarium sp.
  • Onychocola sp.

What are the clinical features of non-dermatophyte mould onychomycosis? 

Non-dermatophyte mould onychomycosis most often only affects one nail; toe nail involvement is 25 times more common than fingernail involvement.

The clinical sub-types of non-dermatophyte mould onychomycosis are similar to dermatophyte nail infections and include:

  • Distal
  • Lateral
  • Subungual
  • Proximal subungual onychomycosis
  • Superficial white onychomycosis
  • Total dystrophic onychomycosis.

Paronychia is often present.

Infection may also lead to various nail colour changes depending on the infecting species. For example, infection with Aspergillus niger typically results in a black nail colour.

What are the complications of non-dermatophyte mould onychomycosis?

  • Total dystrophy of nail
  • Secondary bacterial infection

How is non-dermatophyte mould onychomycosis diagnosed?

As most moulds require the presence of an underlying nail condition to penetrate the nail, definitive diagnosis can be challenging.

The following diagnostic criterion has been established and the presence of 3 or more of the following criteria confirms diagnosis:

  • Positive direct microscopy
  • Absence of a dermatophyte in culture
  • Growth of non-dermatophyte mould in culture
  • Similar growth of the causative agent in repeat culture
  • Positive inoculum count
  • Positive histology.

Recent diagnostic advances for non-dermatophyte onychomycosis include molecular diagnostics using PCR technology.

See also laboratory tests for fungal infections and dermatological investigations and tests.

Scytalidium direct mycology

What is the differential diagnosis for non-dermatophyte mould onychomycosis?

What is the treatment for non-dermatophyte mould onychomycosis?

Mould infections are more difficult to clear than dermatophyte infections and may require a combination of topical and oral therapies to clear the fungal infection.

For mild to moderate disease

For moderate to severe disease

  • Systemic therapy such as itraconazole or terbinafine either as daily dosing or in a pulse regimen (often combined with topical treatment as above).

Other modalities

  • Medical nail avulsion (chemical or surgical) or debridement in combination with antifungal agents as per above.

What is the outcome for non-dermatophyte mould onychomycosis?

Non-dermatophyte mould onychomycosis often requires a longer duration of treatment compared to treatment for dermatophyte nail infection. The possibility of relapse is also higher.

 

Bibliography

  • Gupta AK, Drummond-Main C, Cooper EA, Brintnell W, Piraccini BM, Tosti A. Systematic review of nondermatophyte mold onychomycosis: diagnosis, clinical types, epidemiology, and treatment. J Am Acad Dermatol. 2012;66(3):494-502. doi:10.1016/j.jaad.2011.02.038. Journal
  • Gupta AK, Summerbell RC, Venkataraman M, Quinlan EM. Nondermatophyte mold onychomycosis. Journal of the European Academy of Dermatology and Venereology. 2021 Mar 24. Journal
  • Bongomin F, Batac CR, Richardson MD, Denning DW. A review of onychomycosis due to Aspergillus species. Mycopathologia. 2018 Jun 1;183(3):485–93. Review https://link.springer.com/content/pdf/10.1007/s11046-017-0222-9.pdf
  • Gupta AK, Taborda VB, Taborda PR, Shemer A, Summerbell RC, Nakrieko KA. High prevalence of mixed infections in global onychomycosis. PloS one. 2020 Sep 29;15(9): e0239648. Journal

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