Derm Dilemma by Dylan dominguez , - md candidate , uams class of 2025
A 45-year-old man presents to his primary care physician with a widespread rash across the back , present and slowly spreading for several months . No other areas of the body are involved , and the patient reports associated modest itching and flaking . Examination demonstrates a papulosquamous eruption characterized by erythematous , scaly plaques with crisply demarcated borders and central clearing . Small papulopustules are noted on some of the raised borders .
What is the most likely diagnosis and appropriate intervention / treatment ?
A . A potassium hydroxide mount should be prepared from skin scrapings , and if indicative of tinea corporis , a topical azole antifungal prescribed . B . The rash represents nummular eczema , and a mid-potency topical corticosteroid cream such as triamcinolone acetonide is recommended . C . The patient has psoriasis , which can be effectively managed with a topical vitamin D analog , such as calcipotriene ointment . D . The patient has seborrheic dermatitis , and a mixture of topical hydrocortisone 2.5 % and ketoconazole 2 % cream would be expected to result in improvement . E . The eruption represents impetigo , likely due to resident staphylococci , and should be treated with topical mupirocin ointment .
Answer : A . The patient has tinea corporis , colloquially known as “ ringworm .” The name is a misnomer , as tinea corporis represents a dermatophyte fungal infection . The organism can be transmitted from direct contact with infected individuals or animals or contaminated fomites .
Dermatophytes require keratin from skin , hair , or nails for sustenance and are comprised of filamentous fungi belonging to the genera Trichophyton , Epidermophyton , and Microsporum . Tinea corporis ( infections involving parts of the body other than scalp , face , groin , or feet ) can be associated with any of these organisms but is most often caused by T . rubrum ( approximately 80-90 % of cases ) and occasionally M . canis , when transferred by a cat or dog . Considering that tinea infections are contracted via contact , it is most often transmitted through physical contact with an infected individual , sharing clothing or towels , or participating in a sport with persistent skin-to-skin contact . Highly humid and warm environments strongly encourage infection .
Tinea corporis is most commonly seen in children , with nearly 50 % of cases in the U . S . diagnosed in children < 10 years old , though infection in adults is not uncommon . Genetic predisposition may play a role in contracting the infection and persons who are immunocompromised are also at higher risk of developing the disease . The differential diagnosis of tinea corporis includes other annular cutaneous dermatoses , which typically present on the trunk and proximal extremities including erythema annulare centrifigum , subacute cutaneous lupus erythematosus , and granuloma annulare . Other papulosquamous disorders such as psoriasis , nummular dermatitis , and large-plaque parapsoriasis may at times mimic tinea corporis . Tinea corporis classically presents as an annular lesion ( s ) with a well-defined , raised , scaly border and central clearing . Lesions are often solitary but can be multiple and / or overlapping . Definitive diagnosis is rapidly provided by the observation of segmented , often branching hyphae in skin scrapings utilizing a potassium hydroxide ( KOH ) preparation . A fungal culture can also be performed , though results will be delayed .
Most instances of tinea corporis can be managed with topical therapy ( allylamines or azoles ). Extensive infection warrants consideration of an oral agent such as terbinafine , itraconazole , fluconazole , or griseofulvin .
128 • The Journal of the Arkansas Medical Society www . ArkMed . org