Diagnosing fungal foot infections can be a tricky business and of course, the whole point of making a diagnosis is to confirm what it is and, just as importantly, to ensure that the treatment you are offering will be an effective one. As we know, about 50% of all nail dystrophies are not fungal and it is likely that you will encounter negative results when mycologically testing from time to time, so it is helpful to have, in the back of your mind, alternative reasons why a patient’s nails may appear dystrophic. In this article, I will cover the most common differential diagnoses for fungal nail disease.
Physical trauma is likely to be the most common cause of toenail dystrophy. Feet by their nature are exposed to mechanical forces from the ground, footwear and even tight hosiery. Nail changes can arise from repetitive micro-trauma or frank nail injury and both can lead to permanent nail changes. Careful assessment is needed of the patient’s foot (and toe) posture, gait and footwear. The pattern of toe nails affected is dictated by the mechanisms involved, but usually interactions with footwear are the prime suspect and this may typically favour the longer toes. First and second toe nails are the common candidates for damage followed by the little toe owing to the narrow shaping of the toe box on most shoes. Lesser toe deformities such as claw and mallet toes can also precipitate nail problems. Nails which are traumatised usually show thickening, a reduced growth rate and a uniform discolouration of the nail plate which can lead to suspicion of fungal involvement.
Reduced peripheral blood flow
Poor circulation in the toes is a very common clinical problem, not just for those with arterial disease but also for those with Raynauds disease. Women are also more prone to this (typically the patient has a history of chilblains or generally “cold toes”). Reduction in blood flow to the nail unit can lead to recurrent onycholysis, distal nail detachment and, in time, gradual thickening and discolouration if it persists.
Psoriasis is a common skin disorder affecting the skin and around 50-70% of patients will show some suggestion of nail involvement. So, its good practice to assess your patient. Check if there’s a family history of skin disorders or evidence problems skin lesions elsewhere as patients may not be immediately aware they have the condition, particularly if it is very minor. In a small number of patients, nail changes may be the only sign of the skin disorder.
Typical features in the toenails include onycholysis, onychauxis, sub-ungual debris and hyperkeratosis. Pitting is more common with white spots in the fingernails. Splinter haemorrhages may also be present. The distribution of nail involvement can be entirely random and typically over time the nail condition relapses and remits – unlike fungal infections of the nail which tend to slowly worsen with time if untreated. Visually, the nails may exhibit an oil drop or salmon spot in the nail proximal to the onycholytic zone which is not normally observed in onychomycosis.
This skin condition less commonly affects the nails than psoriasis but nevertheless can lead to nail dystrophy. Typically, longitudinal ridging is the most common feature (onychorrhexis) with occasional thickening or discolouration. Usually there are eczematous lesions close by on the hands and feet so a good patient history and examination can help with the diagnosis.
In this auto-immune condition, adult patients typically developed purple, polygonal papules around the wrists and ankles often accompanied by oral involvement. Lesions are intensely itchy and may persist for some months. Nail changes in this condition are common – around 10% of patients are affected. Typically, the nails become roughened (trachonychia) and may atrophy with scarring although nail thickening has also been reported with accompanying sub-ungual hyperkeratosis.
Increasingly, the repetitive use of nail varnishes and lacquers on the nail can lead to longer term changes. Nail degranulation is a recent phenomenon associated with the use of nail gels and lacquers. Regular application and re-application of harsh chemicals can cause surface changes to the toe nails similar to superficial white onychomycosis so mycological testing is very helpful here. Treating nail degranulation generally just requires the patient to thoroughly remove any residual varnish and have a break from nail varnish for a few months which will help the nail to return to its former glory.
Solitary white spots can also be due to trauma or entirely idiopathic in patients, but these tend to occur within the nail plate and not on the surface of the nail itself unlike superficial white onychomycosis. Pseudomonas infections can occur under the nail, particularly when the feet have been wet for prolonged periods of time. The typical picture is a blue-green area of discolouration located under the nail. Colourwise, this is quite unlike typical onychomycosis which tends to be white-yellow-brown-black.
Twenty Nail Dystrophy
This is a nail disorder, which as the name suggests, affects all 20 nails. Usually arising in childhood the condition, is of unknown aetiology and leads to a widespread trachonychia of all nails (roughing with longitudinal ridging) often referred to as sand papered or sand blasted nails. Occasionally it may accompany known skin disorders such as alopecia and lichen planus. The condition has also been known to spontaneously disappear. Despite the appearance, they are not liable to fungal infection.
Finally, although rare, malignant melanoma can lead to brown discolouration in the nail unit – as a linear pigmented brown-black stripe arising from the nail matrix and progressing distally. Suspicion should be raised particularly in a fair skinned individual with a single digit affected, particularly if the lesion has been evolving or bleeding. Extension of pigment from the nail unit onto the surrounding peri-ungual tissues can also arise and warrants immediate referral for diagnosis and treatment.