What are the diagnostic criteria for alopecia areata?

Diagnostic Criteria for Alopecia Areata

Alopecia areata is diagnosed primarily by its characteristic clinical presentation of well-defined patches of complete hair loss with "exclamation mark" hairs at the periphery of patches, with no need for investigations in most cases. 1, 2

Clinical Features

Primary Diagnostic Features

• Well-defined patches of complete hair loss with normal-appearing skin
• Preserved follicular ostia (hair follicle openings still visible)
• Exclamation mark hairs (short broken hairs) at the periphery of expanding patches 1, 3
• Yellow dots commonly seen on dermoscopy in areas of hair loss 1

Additional Clinical Findings

• Affected skin may be slightly reddened but otherwise appears normal 1
• Nail involvement in approximately 10% of patients 1
• Can affect any hair-bearing skin, not just the scalp 1
• May present in various patterns:
  • Patchy alopecia areata (most common)
  • Ophiasis pattern (band-like hair loss at scalp margin)
  • Diffuse alopecia areata (less common, can be difficult to diagnose)
  • Total scalp hair loss (alopecia totalis)
  • Complete body hair loss (alopecia universalis) 3, 4

Diagnostic Tools

Dermoscopy

Dermoscopy is highly valuable for diagnosis, revealing:

• Regular round yellow dots (common finding)
• Dystrophic hairs with fractured tips (exclamation mark hairs)
• Cadaverized hairs (fractured before emergence from scalp)
• Black dots 1, 2

Hair Pull Test

• Positive pull test (>6 hairs extracted) indicates active disease 2

Differential Diagnosis

Key conditions to distinguish from alopecia areata:

1. Trichotillomania

   • Incomplete hair loss pattern
   • Broken hairs firmly anchored in scalp (remain in anagen phase)
   • Different dermoscopic findings 1

2. Tinea Capitis

   • Scalp inflammation (may be subtle)
   • Often has scaling
   • Fungal culture can confirm diagnosis 1

3. Early Scarring Alopecia

   • Loss of follicular ostia
   • Different dermoscopic pattern 1

4. Telogen Effluvium

   • Diffuse thinning rather than patches
   • No exclamation mark hairs 1

5. Anagen Effluvium (drug-induced)

   • May mimic diffuse alopecia areata
   • History of chemotherapy or toxic exposure 1

6. Systemic Lupus Erythematosus

   • Often has other systemic symptoms
   • May require serology for confirmation 1

7. Secondary Syphilis

   • "Moth-eaten" pattern of alopecia
   • Serology can confirm diagnosis 1

Investigations

Investigations are unnecessary in most straightforward cases of alopecia areata 1. When diagnosis is uncertain, consider:

• Fungal culture (if tinea capitis suspected)
• Skin biopsy (if diagnosis remains unclear)
• Serology for lupus erythematosus (if suspected)
• Serology for syphilis (if suspected) 1

Common Pitfalls in Diagnosis

• Misdiagnosing diffuse alopecia areata: This less common presentation can be confused with telogen effluvium or androgenetic alopecia 1
• Overlooking subtle tinea capitis: Always consider fungal infection, especially in children 1
• Missing coexisting trichotillomania: These conditions can sometimes occur together 1
• Unnecessary laboratory testing: Routine screening for autoimmune diseases is not justified despite associations 1
• Failure to use dermoscopy: This non-invasive tool significantly improves diagnostic accuracy 1, 2

By carefully evaluating these clinical features and using appropriate diagnostic tools when needed, alopecia areata can be accurately diagnosed in most cases without extensive testing.