Review Question - QID 108616

The patient is presenting with a dry, scaly patch that has developed into an area of alopecia, suggesting the diagnosis of Tinea capitis. The best initial diagnostic test for Tinea capitis is a KOH prep.

Tinea capitis is a subacute or chronic dermatophyte infection of the scalp. It classically presents as a scaly patch with resulting patchy alopecia. The lesion will often have an erythematous “active border” and within the patch the hairs will break off at the scalp surface, causing a residual black dot, such as was shown in Figure A of the question stem. Normally, it is minimally symptomatic, but can be itchy. Tinea capitis can be misdiagnosed as similarly presenting conditions. The best initial diagnostic test is a potassium hydroxide (KOH) test. When positive, one will see segmented hyphae, such as shown in Illustration A. If a more accurate diagnosis is necessary, a fungal culture can be done, but this will take days for final results. This patient should be treated with oral terbinafine, itraconazole, or griseofulvin (less commonly used).

Figure A shows Tinea capitis characterized by a scaly patch and resulting hair loss in a black dot pattern. Illustration A shows a KOH preparation of a scalp scraping from a patient with Tinea capitis with its characteristic segmented hyphae.

Incorrect Answers:
Answer 1: A skin biopsy would be a good diagnostic test for systemic lupus erythematosus (SLE), but as there is a clinical suspicion for Tinea capitis, KOH remains the easier and more efficient initial diagnostic test. SLE can present in many ways including discoid lupus of the scalp characterized by erythematous, inflamed, scaling patch(es) which can cause permanent scarring and hair loss. Although the patient has fatigue, she does not have other indications of SLE such as pulmonary or renal symptoms, a malar rash, or a significant family history.

Answer 2: Psychiatric assessment for obsessions and compulsions would be an appropriate initial step in management if the suspected diagnosis was trichotillomania. This behavior is common in patients with OCD which could be suggested by her ritualistic and repetitive combing of her hair. That being said, none of the other symptoms suggest OCD and this behavior started only in response to the symptoms she is experiencing without any other aspect of her life being affected.

Answer 4: A positive Wood’s lamp test can be helpful if Tinea capitis is suspected, but is not diagnostic and also has high rates of false negatives. For instance, the most common cause of Tinea capitis, T. tonsurans, does not fluoresce.

Answer 5: A skin patch test can be used if there is a clinical suspicion for contact dermatitis. Although hair chemicals can cause contact dermatitis, this would have likely affected the entire scalp, rather than a localized lesion. Contact dermatitis, when acute, can be itchy with small erythematous papules or blisters. When chronic, it can present as a thickened, pigmented, scaly lesion.

Bullet Summary:
Tinea capitis often presents with a scaly, erythematous patch on the scalp that may develop into alopecia with residual black dots. The best initial test for diagnosis is a KOH prep, the most accurate test is a fungal culture, and treatment is oral terbinafine, itraconazole, or griseofulvin.