What is alopecia areata?

What is Alopecia Areata

Alopecia areata is an autoimmune condition where T lymphocytes attack hair follicles, causing patchy, non-scarring hair loss that can affect any hair-bearing area of the body, most commonly the scalp. 1

Pathophysiology

• The disease is mediated by T lymphocytes that target hair follicles, disrupting the immune privilege normally protecting these structures 1, 2
• Multiple genetic loci involved in hair follicle maturation and immune processes have been linked to disease development 2
• The hair follicle maintains its potential to regrow hair because it typically does not sustain permanent injury, distinguishing it from scarring alopecias 3

Clinical Presentation

• Patchy hair loss appears as well-defined round or oval areas without scarring or obvious skin changes 1, 4
• Exclamation mark hairs (short broken hairs with tapered proximal ends) are pathognomonic and appear around expanding patches 1, 5
• The disease spectrum ranges from limited patchy involvement to alopecia totalis (complete scalp hair loss) or alopecia universalis (total body hair loss) 2, 3
• Ophiasis pattern involves the scalp margin and carries a poorer prognosis 1
• Nail changes including pitting, ridging, or dystrophy occur in approximately 10% of patients and may precede, follow, or occur concurrently with hair loss 1, 3

Epidemiology

• Lifetime risk is approximately 1.7-2% in the general population worldwide 4, 6
• No sex predominance exists based on formal population studies 6
• About 20% of affected individuals have a family history, indicating genetic susceptibility 1
• First onset most commonly occurs in the third and fourth decades of life, though 60% of patients develop disease before age 20 3, 4, 6
• Earlier age of onset corresponds with increased lifetime risk of extensive disease 6

Associated Conditions

• The disease associates with other autoimmune conditions including thyroid disease, lupus, and vitiligo 1
• Patients are at increased risk for atopy (asthma, allergic rhinitis, atopic dermatitis) 3, 6
• Depression and anxiety are common comorbidities, with a bidirectional relationship where psychological symptoms can both result from and potentially exacerbate hair loss 2, 6

Diagnosis

• Diagnosis is typically made clinically without laboratory workup in most cases 1
• Dermoscopy is the single most useful non-invasive diagnostic tool, revealing yellow dots (most common feature, present in 6-100% of patients), exclamation mark hairs, cadaverized hairs, and black dots 1, 7
• Yellow dots that are regularly round indicate active disease progression 7
• A positive pull test at margins of expanding areas signals active disease 1
• Laboratory testing is indicated only when diagnosis is uncertain, presentation is atypical, or when ruling out other conditions in the differential diagnosis 1

Natural History and Prognosis

• 34-50% of patients recover within one year without treatment, making spontaneous remission common 1, 5
• However, 14-25% progress to total scalp or body hair loss 1
• Childhood onset and ophiasis pattern carry poorer prognoses 1
• Patients with less than 25% hair loss initially have a 68% chance of being disease-free at follow-up, compared to only 8% for those with more than 50% initial hair loss 7
• Disease severity at presentation is the strongest predictor of long-term outcome 7

Common Pitfalls

• Avoid ordering excessive laboratory tests when the diagnosis is clinically evident 1
• Do not overlook dermoscopy as a valuable non-invasive diagnostic tool that can provide definitive findings 1
• Failing to assess for psychological impact is a common error, as the condition may cause considerable psychological and social disability warranting evaluation for anxiety and depression 1, 2
• Do not assume the condition is permanent—many cases are self-limited with high rates of spontaneous recovery 1, 5