A toddler presents with patchy hair loss
Given the history of sudden hair loss, with the exam revealing a well-circumscribed patch of focal alopecia without cutaneous inflammation, hairs with a narrow base and broad distal shaft, the diagnosis is alopecia areata (AA).
Alopecia areata (AA) is a nonscarring alopecia, within a set of diseases characterized by the preservation of hair follicles and therefore the potential for future hair regrowth.1 AA is believed to be caused by a breakdown of the immune-privileged nature of hair follicles, resulting in T-lymphocytes targeting the hair follicle directly, shifting follicles to early catagen or telogen phase, but sparing follicular stem cells, thereby allowing the follicle to regenerate in the future.1-3 Risk factors include family history of AA, thyroid disorders, as well as iron and vitamin D deficiency.4,5 It characteristically presents with focal, well-demarcated patches of hair loss in the scalp, typically with background skin normal to slightly pink.3,6 Exam can show “exclamation point” hairs consisting of hairs that are narrow at their base and wide at the distal end.3,7 Patients may also exhibit eyebrow and eyelash loss as well as nail changes including nail pitting and splitting.8 Diagnosis is typically made clinically but is supported by a positive hair pull test, where hairs are pulled from the periphery of an alopecic lesion; the presence of greater than 10% of hairs plucked from the scalp indicates a positive result.9,10
What’s the differential diagnosis?
The differential diagnosis of AA includes other nonscarring alopecias such as trichotillomania and telogen effluvium. Other possible diagnoses include lichen planopilaris and tinea capitis.
Trichotillomania results in irregularly bordered hair loss and broken hairs of different lengths because of an internal urge to remove one’s hair, resulting in nonscarring alopecia. It can be associated with obsessive-compulsive disorder, anxiety, or other body-altering behaviors like skin picking and nail biting (characterized as body-focused repetitive behavior disorders). Treatments include reassurance and education, behavior modification, or systemic therapy including tricyclic antidepressants or SSRIs. Toddlers can engage in hair pulling behavior and trichotillomania can be difficult to differentiate from AA. However, the absence of broken hairs of varying lengths makes trichotillomania less likely in this patient.
Telogen effluvium is another form of nonscarring alopecia that presents as diffuse hair thinning across the entire scalp in response to acute psychological or physiological stress, hormonal changes, certain medications, systemic illness, or nutritional deficiency. The timing between the triggering event and hair loss can vary from weeks to months. Diagnosis requires detailed history-taking and may include evaluation for endocrinologic hair thinning (e.g. thyroid function tests) to identify reversible causes. Treatment involves directing therapy to the underlying etiology and most cases of telogen effluvium are self-limited. The presence of a well-circumscribed patch of hair loss in this patient makes AA more likely.
Lichen planopilaris (LPP) is a scarring, irreversible alopecia caused by T-lymphocytes attacking follicular hair stem cells. It is characterized by hair loss, pruritus, burning pain, scalp scaling, and multifocal scarring. Exam shows patches of alopecia with loss of follicular ostia centrally and perifollicular scale and erythema at the borders. Diagnosis is aided by biopsy of the affected scalp. Treatment of LPP requires the use of potent and superpotent topical corticosteroids and intralesional corticosteroids to decrease scalp inflammation and prevent further progression. The presence of follicular ostia and absence of perifollicular scale in this patient makes LPP highly unlikely.
Tinea capitis is a fungal infection of the scalp caused by dermatophytes including Trychophyton tonsurans and Microsporum canis. It presents with patches of alopecia with overlying scale and broken hairs and can have associated cervical and occipital lymphadenopathy. Diagnosis can involve skin scraping and KOH prep to visualize branching hyphae as well as fungal culture to identify the causative organism. Because dermatophytes in tinea capitis invade hair follicles, topical antifungals are ineffective because of their lack of penetration. Therefore, systemic antifungals including oral terbinafine and griseofulvin are considered first-line agents for treatment.
