The correct answer is dermatophytosis (choice “a”). Not only will the common dermatophytic fungi not cause redness and swelling under and around a nail, but had that been the cause, there would almost certainly have been a positive response to two months’ treatment with terbinafine. Therefore, dermatophytosis was not under serious consideration as the cause of this patient’s complaint.
The other choices were all possible explanations for his problem. See discussion below for details.
The commonly encountered dermatophytic fungal organisms are incapable of provoking this type of response in an immunocompetent person. However, that proviso does not apply to the yeast family—in particular, candida (choice “c”). This case demonstrates why candida should be considered separately from the dermatophytes. Candida will not grow on culture media designed for dermatophytes, and the diseases it produces will not respond to allylamines, of which terbinafine is the chief example. But most importantly, from a clinical standpoint, candida is quite capable of producing considerable redness and swelling focally because of the body’s immune response to its antigen.
Neoplasia (choice “b”) of soft tissue or bone was rightly considered in this case, especially in light of the lack of tenderness. Glomus tumors, though typically tender to touch, often arise in the nail bed. Squamous cell carcinoma (choice “d”), especially that caused by human papillomavirus, and even melanoma can present in this way.
The culture performed on the pus obtained from under this nail confirmed the presence of candida in large numbers. Subsequent treatment with fluconazole (200 mg/d for a month) was successful. Since this finding is unusual in men, a random blood sugar measurement was taken; the result (310 mg/dL) prompted referral to the patient’s primary care provider.
Had the patient not responded to the fluconazole, the next step would have been removal of the nail and possible biopsy of the underlying tissue. X-rays are mandatory in such cases, to rule out the bony changes of osteomyelitis or cancer. The cultures for acid-fast bacilli were negative, but atypical mycobacteria have been implicated in such cases.