Pseudomonas Aeruginosa Nail Infections
Author: Sayeda Nahar
Chief Editor: Dr Daniel Keith
Also known as 'Green Nail Syndrome'
Introduction
Pseudomonas aeruginosa is an aerobic, Gram-negative, coccobacillus, rod-shaped bacterium commonly found in water and soil. It is also transiently present on the skin and readily colonises moist environments. Serious and systemic infections caused by Pseudomonas aeruginosa generally occur in individuals who are immunocompromised, have damaged tissues, or artificial lines. As such, high-risk patient populations include those with malignancies, HIV/AIDS, burns, diabetes, indwelling urinary catheters, or following trauma or surgery.
Pseudomonas aeruginosa can lead to both local and systemic infections. Infection of the nail presents as a characteristic green or yellow-green discolouration (chloronychia), coining the term “Green Nail Syndrome”. This pigmentation is due to the accumulation of pyoverdine and pyocyanin, produced by the bacterium that adheres to the undersurface of the nail plate along with debris. Typically, the infection affects one or two digits.
Aside from the characteristic green colouration, the infection may be asymptomatic, though it can cause pain due to the action of bacterial proteases on the nail bed epithelium.
Risk Factors
There are various risk factors which increase the likelihood of this infection including:
Onycholysis refers to the abnormal separation of the nail from the nail bed, resulting in the loss of the waterproof seal typically formed by the skin at the nail’s base. This detachment creates a subungual space where dirt and debris can accumulate, providing an entry point for bacterial pathogens. Trauma to the nail or surrounding area can predispose individuals to the development of onycholysis.
It is also important to note that chronic exposure to water increases the risk of infection due to moist and damp environments, which facilitate bacterial colonisation. As such, individuals whose occupations involve frequent contact with water – such as homemakers, barbers, swimmers, dishwashes, bakers, and healthcare workers – are at increased risk for developing onycholysis and related infections.
Diagnosis
Diagnosis is typically based on the presence of key clinical features, including chloronychia (green pigmentation caused by the production of pyocyanin and pyoverdine), as well as paronychia or onycholysis. Routine dermoscopy is recommended to aid in diagnosis. Although not essential for confirming the diagnosis, additional supportive tests, such as nail plate clippings for histological examination and Gram staining, or a wound culture from the affected area, may be performed.
Dermoscopic Appearance
Anectodally, Pseudomonas aeruginosa infection presents as a yellow-green discolouration with a fading border in cases of onycholysis, and as a green discolouration near an oedematous proximal nail fold in chronic paronychia.
Wood’s lamp (UV dermoscopy) is a useful diagnostic tool for evaluating fungal and bacterial infections, pigmentary conditions, and metabolic disorders. In the context of Pseudomonas aeruginosa infection, Wood’s lamp examination typically reveals a characteristic green fluorescence, which is attributable to the presence of pyoverdin. This finding is crucial for distinguishing P.aeruginosa infections from melanomas, which would exhibit dark brown, black, or blue-white fluorescence due to the presence of melanin.
The images below demonstrate a Pseudomonal green nail under normal lighting (images A and B) and under Wood’s lamp (image C).
Differentials
Important differentials to exclude are stated as below with distinguishing features detailed. It is key to identify correct diagnosis to avoid unnecessary biopsies.
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Subungual haematoma
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Subungual melanoma
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Onychomycosis
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Exogenous pigment
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Chemical exposure to solutions containing pyocyanin or pyoverdin
The table below details features of differentials, categorised into neoplastic, traumatic, infective, idiopathic/congenital and drug-induced causes, which can be compared to features of Pseudomonas Aeruginosa Nail Infection to come to a more definitive diagnosis. This is important as can help easily exclude more sinister pathologies (i.e., melanoma) and provide patients with reassurance of this.
