Utility of Wood's Lamp in Intertrigo

Sir,

Intertrigo is caused due to friction on opposing skin surfaces in adjunct with moisture trapped in the skin folds. It presents as chronic erythematous desquamation associated with malodor, maceration, variable edema, and vesiculopustular lesions. Associated symptoms include burning, pruritus, or pain.[1] We report a case of gram-negative toe web infection wherein Wood's lamp proved as a noninvasive and cost-effective diagnostic modality, helping in early and accurate diagnosis.

A 52-year-old male presented with pruritic macerated superficial erosion of the first interdigital space of the right foot for 6 months duration. The affected area was sharply demarcated from the normal skin and showed maceration with reddish granulation tissue at the base [Figure 1a and b]. There were no satellite lesions. The nail of the great toe appeared dystrophic. The patient was treated with antifungals (tab fluconazole and topical sertaconazole) with a provisional diagnosis of erosio interdigitalis blastomycetica. Other differentials included causes of nonhealing erosions such as cutaneous tuberculosis, leprosy, chronic insult dermatitis, and ulcerative lupus vulgaris. No clinical improvement was seen after 2 weeks.

Figure 1.

(a) Maceration in the first interdigital space of the right foot. (b) Plantar aspect of the interdigital space

Before culture was sent, we conducted few bedside tests including a 10% potassium hydroxide (KOH) mount and Wood's lamp. The former was negative, however, surprisingly Wood's lamp showed a clear greenish fluorescence over the lesional area with patchy coral-red fluorescence [Figure 2a]. Greenish fluorescence on Wood's lamp indicates tinea pedis and Pseudomonas infection.[2]

Figure 2.

(a) Greenish fluorescence (green arrow) in the lesional skin with patchy red fluorescence (red arrow). (b) Visible reduction at end of 10 days

Since KOH ruled out tinea pedis, a diagnosis of mixed Pseudomonas and Corynaebacterium (coral red fluorescence) was made. The diagnosis was confirmed by Pseudomonas sps. growth on culture. The patient was started on oral ciprofloxacin 500 mg BD and topical nadifloxacin for 10 days, after which there was distinct clinical improvement [Figure 2b]. The patient was advised to keep the feet dry by using talcum powder.

Such clinical presentations have been reported with other gram-negative bacteria including Pseudomonas[3] and also Corynaebacterium.[4]

Pseudomonas exhibits greenish fluorescence due to the pigment pyoverdin (or fluorescein).[5] Our case demonstrates the unfamiliar but handy use of Wood's lamp in the diagnosis of chronic erosions, sparing the need for more complex time consuming, and expensive modalities-like culture.

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Conflicts of interest

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