Abstract
We present two patients highlighting the importance of distinguishing tinea corporis from psoriasis.
Patient 1
A 41-year-old female with a background of inflammatory arthritis on methotrexate developed an intensely itchy erythematous patch on her right foot. It was felt by her Rheumatologists to be psoriasis and her arthritis was redefined as psoriatic arthritis. Her father had psoriasis. However, it failed to respond to topical steroids or calcipotriol from her GP and she was referred to dermatology.
In the dermatology clinic, she was found to have several annular well-demarcated erythematous lesions on the thighs and lower legs. On both of her feet there was well-demarcated erythema, which the patient told us was extending. There was toenail dystrophy consisting of thickening of nails and friable, crumbly distal nails.
Skin scrapings and toenail clippings confirmed Trichophyton rubrum. The lady was commenced on oral terbinafine. After 8 weeks, the lesions had considerably reduced in size and were much less pruritic. Treatment was continued for a total of 3 months.
Patient 2
A 43-year-old female with a family history of psoriasis was referred to our department for phototherapy by the dermatology community nurse specialist, following a 1-year history of an eruption diagnosed as chronic plaque psoriasis. Topical steroids and Dovobet had produced attenuation of the skin signs but not clearance.
The rash had started on the right buttock and had spread rapidly. Skin scrapings taken from the right buttock in the community had been reported as negative.
Phototherapy was commenced, but failure to progress during the phototherapy prompted clinical review. On examination there was an extensive erythematous scaly area to the buttocks and lower back, and other annular erythematous patches to the thighs, with occasional pustules especially at the edges (Figs 1 to 3.) There was pitting to two fingernails.
Patient 2, right leg. This demonstrates the well-defined, scaly, erythematous lesions, and the scale is clearly more predominant at the edges of the lesions. Patient 2, buttocks and lower back. This demonstrates the well-defined, scaly, erythematous lesions, and the scale is clearly more predominant at the edges of the lesions. Patient 2, right hip/lateral thigh. This demonstrates scaly plaques with a pronounced rim of scale at the edge of the lesion, within which some pustules are visible – typical for tinea incognito.
Subsequent skin scrapings confirmed Trichophyton rubrum and biopsy was consistent with tinea corporis. A diagnosis of tinea incognito was made and topical steroids and phototherapy were stopped and the patient was commenced on itraconazole 100-mg daily for 2 weeks. Six weeks later there was resolution of the inflammatory dermatitis with only post-inflammatory changes remaining.
Discussion
It can be difficult to clinically distinguish between psoriasis and tinea corporis. Both are characterised by well-demarcated areas of erythema with scaling. Annular lesions that are expanding slowly without waxing and waning are highly suggestive of tinea infection. Often with tinea, the scaling and erythema are more pronounced at the advancing edge of the lesions (Cunliffe, 2014). The scaling in tinea corporis may be finer than the thick silvery scale of psoriasis. Fungal infections often start at one site (commonly the foot) and spread sequentially to other areas. Nail pitting and family history are indicators of psoriasis.
Tinea incognito is the name given to tinea infection that has an altered clinical appearance due to the use of topical steroids. The pustules at the edge of the lesions in our second patient were a typical sign of tinea incognito. Tinea incognito is also less scaly than untreated tinea corporis (Oakley, 2003). Topical steroids reduce inflammation, therefore the patient often reports improvement in itch, but this flares on stopping the steroid, encouraging the patient to restart them. Topical steroids not only modify the appearance of the rash making diagnosis difficult, but also encourage spread of the infection.
Tinea incognito is a relatively common reason for referral to dermatology. These two cases were unusually extensive and show that the diagnosis can be missed by both secondary care and specialist nurse teams. They also demonstrate how patients can follow a treatment pathway without further questioning the diagnosis.
Scrapings for mycology should be sent for all patients with scaly lesions in whom there is any diagnostic uncertainty, preferably before application of a topical steroid, especially in those who fail to respond to usual treatments, or those who have risk factors for tinea corporis e.g. immunosuppression. It is vital that an adequately large sample of scrapings is obtained to maximise the chances of a diagnosis. Scrapings should be taken from multiple sites if there are multiple scaly lesions, and if there is an obvious advancing edge then scrapings should be obtained from that edge. Scrapings in tinea incognito may be falsely negative and biopsy is sometimes needed to confirm the diagnosis.
For non-extensive cases of tinea corporis, the National Institute for Health and Care Excellence (NICE) recommends topical clotrimazole, econazole or miconazole. For extensive disease, oral terbinafine, griseofulvin, or itraconazole are recommended, depending on any relevant contraindications for each individual patient (NICE, 2014) Tinea incognito must also be treated with systemic antifungals as it is unresponsive to topical agents.