1. Presented by Jason Denney, MD and reviewed by Sean Zhang, MD, PhD

Case vignette

An elderly patient presents for evaluation of an itchy rash on their face and neck. The patient wears a CPAP mask at night but otherwise has no significant past medical history. The rash began nearly a year prior to presentation. The patient had been seen by their primary care physician and treated with topical steroids and benadryl cream for presumed eczema. However, the rash persisted. Physical exam revealed a pink dermal annular and arcuate patches on the lateral neck and lateral malar eminences. A skin scraping and KOH prep was performed and was negative in the dermatology clinic. Due to this finding, a contact dermatitis or a dermal granulomatous process was clinically suspected and he was treated with a trial of 0.5% desonide cream. After six weeks, the rash had not completely resolved and two punch biopsies were performed on the lateral neck. These punch biopsies revealed a subacute spongiotic dermatitis and a differential diagnosis of nummular eczema, contact dermatitis, artopic dermatitis, erythema annulare centrifugum and dermatomycosis was raised. A PAS-F stain performed on the histologic sections revealed fungal hypae in the superficial parakeratosis layers (shown at left) and a diagnosis of tinea faciei was made. The patient was started on topical terbinafine cream, but in two weeks had not had significant improvement in symptoms and was switched to PO terbinafine for a four-week course.



Question:
Based on epidemiologic data, what is the most common organism to be isolated from this skin scraping?