Nail Unit Disorders



Nail Unit Disorders


Amanda Zubek



The nail is an often-overlooked cutaneous appendage that can exhibit signs of a number of primary dermatoses, both inflammatory and infectious. Nail art, cosmeceuticals, and manicuring comprise a large proportion of the cosmetic industry, and nail disease causes a great deal of distress to patients suffering from primary and secondary nail disorders. This chapter will focus on the most common forms of nail disease, diagnostic approaches, and recommendations for management.



ONYCHOMYCOSIS


BACKGROUND

Onychomycosis is the most prevalent nail disorder worldwide, estimated to comprise 50% of all nail disorders, with a prevalence ranging from 2% to 18% worldwide, but some reports estimate up to 30%.1,2 Men are more commonly affected than women, and incidence increases with increasing age. Toenails are more commonly affected than fingernails, and there is a high rate of comorbid tinea pedis. Onychomycosis is considered a form of superficial mycosis, with the most common causative agent being the dermatophyte, comprising 90% of nail fungal infections. Onychomycosis is notoriously difficult to treat and maintain long-term mycological cure. Patient risk factors include increasing age, poor circulation, diabetes, smoking, nail trauma, immunosuppression, poor nail hygiene. Other patient factors such as drug-drug interactions, behavioral practices, and biochemical properties of the nail plate make treatment challenging.


PRESENTATION

Patients present with a variety of examination findings depending on the clinical subtype of onychomycosis. Common presentations include nail thickening, distal or lateral onycholysis, subungual keratinaceous debris, focal leukonychia, yellow or brown discoloration of the nail, proximal white subungual streaks, complete nail crumbling, and periungual scaling.




PATHOGENESIS

Several organisms can cause onychomycosis. The majority of cases of onychomycosis are caused by the dermatophyte group of fungi, including Trichophyton, Epidermophyton, and Microsporum, which are responsible for 90% of onychomycosis cases. The most common causes are Trichophyton rubrum and Trichophyton interdigitale. Less commonly, Candida yeast and NDMs can cause onychomycosis. Mixed infections can also occur, particularly when it is a dermatophyte and an NDM or Candida yeast. Until recently, it was controversial whether the NDMs and Candida are pathogenic in onychomycosis, but it is now becoming accepted that they can indeed be causative agents and, in some cases, represent particular challenges in treatment. It is important to determine the causative species because treatment decisions will depend on what organism is being targeted.1,2

Onychomycosis occurs when a fungus invades the nail plate. Dermatophytes and other fungi secrete keratinases, elastases, acid proteases, and other proteases, which breakdown the keratin in the nail plate and allow for invasion. The clinical presentation varies based on the anatomic location of the initial invasion. For example, DLSO is caused by distal invasion of the fungus from the hyponychium and lateral nail folds. PSO is caused by proximal invasion through the eponychium, and SWO is due to superficial plate invasion.

Once the nail has been invaded by the fungus, it becomes weak with increased spaces within the compact keratin of the nail plate, allowing for dystrophy, loss of attachment to the nail bed (onycholysis), decreased structural integrity (crumbling), and invasion of surrounding skin (tinea pedis).

Common species of pathogenic fungi include the dermatophytes: T. rubrum, Trichophytum menagrophytes, T. interdigitale, Epidermophyton floccosum; NDMs: Acremonium spp., Alternaria spp., Aspergillus spp., Botryoduplodia spp., Scytalidium hyalinum, Scytalidium dimidiatum, Cladosporum spp., Scopulariopsis spp.; yeast: Candida albicans, Candida parapsilopsis, and Candida tropicalis.

Jun 29, 2020 | Posted by in Dermatology | Comments Off on Nail Unit Disorders
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