Alopecia Areata
Non-fungal patchy hair loss is termed alopecia areata 1.
Definition and Key Features
Alopecia areata is a chronic autoimmune condition characterized by non-scarring, patchy hair loss that can affect the scalp, face, or any hair-bearing area of the body 1, 2, 3. The condition is distinguished from fungal infections (tinea capitis) by the absence of scalp inflammation and specific diagnostic features 1.
Diagnostic Characteristics
The diagnosis is typically straightforward and based on clinical presentation 1. Key distinguishing features include:
- Well-demarcated patches of complete hair loss without scarring
- Exclamation mark hairs - dystrophic hairs with fractured tips visible on dermoscopy 1
- Yellow dots on dermoscopy indicating active disease progression 1
- Cadaverized hairs - hairs fractured before emerging from the scalp 1
Differential Diagnosis
When the diagnosis is uncertain, distinguish alopecia areata from 1:
- Tinea capitis (fungal) - scalp shows inflammation, though signs may be subtle; requires fungal culture
- Trichotillomania - incomplete hair loss with firmly anchored broken hairs still in anagen phase
- Early scarring alopecia
- Telogen effluvium
- Systemic lupus erythematosus
- Secondary syphilis
Pathophysiology
The condition results from T lymphocyte-mediated attack on hair follicles, with collapse of the hair follicle's immune privilege 1, 2. Approximately 20% of patients have a family history, indicating genetic predisposition involving MHC and cytokine genes 1.
Clinical Spectrum
- Patchy alopecia areata - most common form, affecting approximately 80% of patients 2, 4
- Alopecia totalis - complete scalp hair loss
- Alopecia universalis - complete body hair loss
Diagnostic Workup
Investigations are unnecessary in most cases 1. When diagnosis is uncertain, consider:
- Fungal culture (to exclude tinea capitis)
- Skin biopsy showing peribulbar lymphocytic infiltrate ("swarm of bees" pattern) 4
- Serology for lupus or syphilis if clinically indicated
Routine screening for autoimmune diseases or iron deficiency is not recommended, as evidence does not support treatment benefit 1.