Onychomycosis
Author: Dr Lizzy Wasson
Chief Editor: Dr Daniel Keith
Onychomycosis describes a fungal nail infection, affecting both fingernails and toenails. It can be seen more commonly those who are immunocompromised, older, smokers or have comorbidities such as diabetes. It may also be seen in patients who are athletes or use communal changing rooms.
The most common pathogens associated with Onychomycosis are dermatophytes. These are organisms that break down keratin. The most common dermatophytes to cause nail infection are Trichophytum Rubrum and Trichophytum Interdigitale, for which secondary infection with pseudomonas is common. A small number of cases are due to non-dermatophyte infections and this may include moulds and yeasts.
Macroscopic Appearance
The key macroscopic features of Onychomycosis are premature distal crumbling of the nail, lifting of the nail bed (onycholysis) and discolouration of the nail. Discolouration of the nail can be in a variety of colours, but the most common are yellow, red and brown.
This photograph has been provided courtesy of Dr Nick Halsey, GP.
Dermoscopic Appearance
Features of the macroscopic appearance can be examined more closely using a dermatoscope.
At the distal aspect you may see crumbling of the diseased nail also known as ‘distal irregular termination’. From a distal view point you may also notice subungual hyperkeratosis leading to a thicker, irregular appearance of the ventral nail surface, this is known as a ‘ruin’ appearance. Clumping of material known as sulphur deposits may also be seen.
Onycholysis presents as a whitening of the nail as it lifts from the nail bed. In Onychomycosis this most commonly presents with a ‘spiked’ pattern, meaning the boundary between normal nail and onycholytic nail is irregular.
Along with discolouration of the nail(chromonychia), under the dermatoscope you may also be able to visualise ‘longitudinal striae’ or lines along the nail. This can be differentiated from other causes of melanonychia by the ‘reverse triangle sign’ meaning that the band of colour becomes wider more distally in the nail. This contrasts melanomas which demonstrate the ‘triangle sign’ and are wider closer to the nail bed.
This photograph has been provided courtesy of Dr Nick Halsey, GP.
Wood's Lamp
Wood’s lamp uses UVA ultraviolet light to visualise many dermatological conditions. Normal skin and nail will show a light blue hue under Wood’s lamp. However, many fungal pathogens will fluoresce under wood’s lamp allowing diagnosis of onychomycosis. Furthermore, Wood’s lamp can be particularly useful when debriding a fungal nail as it allows clear identification of the disease borders.
