How is diffuse alopecia areata differentiated from other forms of alopecia?

Differentiating Diffuse Alopecia Areata from Telogen Effluvium and Androgenetic Alopecia

Diffuse alopecia areata is distinguished from telogen effluvium and androgenetic alopecia primarily through dermoscopy findings (yellow dots, exclamation mark hairs, cadaverized hairs), clinical course, and when necessary, scalp biopsy. 1, 2

Key Diagnostic Features

Dermoscopy (Most Practical First-Line Tool)

Dermoscopy is the single most useful non-invasive tool to differentiate these conditions at the bedside. 1, 3

• Diffuse alopecia areata shows:

  • Regular round yellow dots (present in 6-100% of cases, indicating active disease) 1, 3
  • Exclamation mark hairs (dystrophic hairs with fractured tips) 1, 3
  • Cadaverized hairs (hairs fractured before emergence from scalp) 1, 2
  • Black dots (present in 0-84% of cases) 3

• Telogen effluvium shows:

  • Absence of yellow dots and exclamation mark hairs 1, 2
  • Diffuse thinning without specific dermoscopic markers 2

• Androgenetic alopecia shows:

  • Hair pattern with diffuse thinning at crown and frontal hairline preservation 2
  • Absence of exclamation mark hairs and yellow dots 1, 3

Clinical History Patterns

The temporal pattern and triggers clearly separate these conditions. 2, 4

• Diffuse alopecia areata:

  • Unpredictable course with potential for spontaneous remission (34-50% recover within 1 year) 1, 2
  • May have personal or family history of autoimmune disease (20% have family history) 1, 2
  • Nail changes present in approximately 10% of patients (pitting, ridging, dystrophy) 1, 2

• Telogen effluvium:

  • Clear triggering event 2-3 months prior (illness, surgery, childbirth, severe stress, rapid weight loss) 2
  • Self-limited course with 80% spontaneous resolution once trigger eliminated 2, 5
  • No nail involvement 2

• Androgenetic alopecia:

  • Gradual progressive onset without acute triggers 2, 4
  • Pattern distribution (crown thinning with frontal preservation in women) 2
  • No nail changes 2

Physical Examination Findings

The pull test and hair distribution pattern provide immediate clinical differentiation. 1, 6

• Diffuse alopecia areata:

  • Positive pull test at margins of expanding areas signals active disease 6
  • Preserved follicular ostia (non-scarring) 6
  • White hairs may be spared initially 6

• Telogen effluvium:

  • Positive pull test diffusely across entire scalp 2, 4
  • No exclamation mark hairs 1, 2

• Androgenetic alopecia:

  • Negative pull test (hairs firmly anchored) 4
  • Miniaturization of hair shafts in affected areas 4

When Biopsy is Necessary

Scalp biopsy should be performed when dermoscopy and clinical features remain inconclusive after initial evaluation. 1, 7

• Biopsy is particularly indicated when diffuse alopecia areata presents atypically without characteristic dermoscopic findings 1, 2
• The British Journal of Dermatology emphasizes that diffuse alopecia areata can be diagnostically challenging and may require histopathologic confirmation 1
• Dermoscopy helps select the optimal biopsy site when needed 3

Laboratory Testing Algorithm

Laboratory tests help exclude mimicking conditions but do not definitively diagnose diffuse alopecia areata. 1, 2

First-Line Tests (When Diagnosis Uncertain):

• Fungal culture - to exclude tinea capitis (scalp may show subtle inflammation) 1, 2
• Serum ferritin - levels <60 ng/mL indicate iron deficiency causing telogen effluvium 2, 5
• TSH - to exclude thyroid disease mimicking diffuse hair loss 2, 5
• Vitamin D level - 70% of alopecia areata patients are deficient (<20 ng/mL) versus 25% of controls, though this supports rather than diagnoses 2

Additional Tests if Indicated:

• Serology for lupus erythematosus - when systemic lupus is suspected 1
• Serology for syphilis - when secondary syphilis is in differential 1
• Hormonal panel (testosterone, SHBG) - if signs of androgen excess suggest androgenetic alopecia 2, 5

Common Diagnostic Pitfalls

The most frequent error is failing to use dermoscopy, leading to unnecessary testing or misdiagnosis. 1, 3

• Ordering excessive laboratory tests when dermoscopy clearly shows yellow dots and exclamation mark hairs pathognomonic for alopecia areata 2, 3
• Mistaking early diffuse alopecia areata for telogen effluvium without dermoscopic examination 1, 7
• Overlooking nail examination, which provides supportive evidence for alopecia areata when pitting or dystrophy is present 1, 2
• Failing to document findings photographically through dermoscopy for objective follow-up assessment 3

Practical Clinical Algorithm

1. Perform dermoscopy first - look specifically for yellow dots and exclamation mark hairs 1, 3
2. If characteristic dermoscopic features present - diagnose diffuse alopecia areata clinically without biopsy 1, 3
3. If dermoscopy inconclusive - obtain targeted laboratory tests (ferritin, TSH, fungal culture) to exclude telogen effluvium triggers and tinea capitis 1, 2
4. If diagnosis remains uncertain after dermoscopy and labs - proceed to scalp biopsy for definitive histopathologic diagnosis 1, 7

The clinical course often reveals the true diagnosis over time, as diffuse alopecia areata follows an unpredictable pattern while telogen effluvium resolves once triggers are addressed. 1, 2