What is the diagnostic workup for diffuse hair loss on the scalp?

Diagnostic Workup for Diffuse Hair Loss on the Scalp

The diagnostic workup for diffuse scalp hair loss should include trichoscopy, a hair pull test, targeted laboratory testing (complete blood count, ferritin, thyroid stimulating hormone, vitamin D), and scalp biopsy when physical findings are inconclusive or suggest scarring alopecia. 1

Initial Assessment

History

• Onset and progression of hair loss (sudden vs. gradual)
• Recent triggering events (childbirth, surgery, high fever, medications)
• Family history of hair loss
• Medical conditions (thyroid disorders, iron deficiency, autoimmune diseases)
• Medications (chemotherapy, anticoagulants, retinoids, antithyroid drugs)
• Hair care practices and styling habits

Physical Examination

Key diagnostic features to identify:

• Pattern of hair loss (diffuse vs. localized)
• Presence of scalp inflammation, scaling, or scarring
• Hair shaft abnormalities
• Signs of specific conditions:
  • Androgenetic alopecia: central thinning, widening of part line
  • Telogen effluvium: diffuse thinning without specific pattern
  • Alopecia areata: well-defined patches with "exclamation mark" hairs
  • Trichotillomania: irregular patches with broken hairs of varying length
  • Tinea capitis: scaly patches with inflammation
  • Frontal fibrosing alopecia: receding frontotemporal hairline with scarring

Diagnostic Tests

Non-invasive Tests

1. Trichoscopy/Dermoscopy (highest priority)

   • Reveals specific features with high diagnostic accuracy 1:
   • Yellow dots, black dots, exclamation mark hairs
   • Hair shaft diameter variation
   • Increased proportion of vellus hairs
   • Decreased follicular units

2. Hair Pull Test

   • Technique: Grasp 50-60 hairs between thumb and index finger and gently pull
   • Positive result: >6 hairs extracted 1
   • Helps assess active shedding

3. Documentation

   • Baseline photographs of affected areas
   • Hair density measurements
   • Terminal-to-vellus hair ratio 1

Laboratory Testing

The American Academy of Dermatology recommends targeted laboratory testing 1:

• Complete blood count
• Ferritin levels (iron deficiency is a common cause)
• Thyroid stimulating hormone
• Vitamin D 25OH levels

Additional tests based on clinical suspicion:

• Hormonal panel (testosterone, DHEAS, androstenedione) if androgenic alopecia suspected
• Antinuclear antibodies if autoimmune disease suspected
• Zinc levels if deficiency suspected

Definitive Testing

Scalp Biopsy

• Indicated when:
  • Physical examination findings are inconclusive
  • Scarring alopecia is suspected
  • To differentiate chronic telogen effluvium from female pattern hair loss 1, 2
• Technique: 4mm punch biopsy, including subcutaneous fat
• Histopathology can reveal:
  • Terminal-to-vellus hair ratio (T:V < 4:1 indicates FPHL) 2
  • Inflammation patterns
  • Scarring/fibrosis

Diagnostic Algorithm

1. Determine if hair loss is diffuse or patchy

2. If diffuse:

   • Perform trichoscopy and hair pull test
   • Order basic laboratory tests
   • Consider most common causes:
     • Androgenetic alopecia (gradual onset, pattern distribution)
     • Telogen effluvium (acute onset 2-3 months after trigger) 2
     • Chronic telogen effluvium (excessive shedding without obvious cause) 2

3. If patchy:

   • Consider alopecia areata, trichotillomania, tinea capitis
   • Perform trichoscopy and appropriate tests (fungal culture for tinea)

4. If scarring is present:

   • Urgent referral to dermatology
   • Scalp biopsy is essential

Common Pitfalls and Caveats

• Misdiagnosis: Chronic telogen effluvium is often confused with female pattern hair loss and can be reliably differentiated only through biopsy 2
• Incomplete workup: Failing to check ferritin and thyroid function even in the absence of obvious clinical features of deficiency/disorder 1, 2
• Premature reassurance: Telling patients hair loss is "just stress" without proper evaluation
• Delayed diagnosis: Scarring alopecias require prompt diagnosis as hair loss may be permanent
• Overlooking psychological impact: Hair loss significantly affects quality of life and may require psychological support 1, 3

Remember that while the initial workup can often be performed by primary care physicians, patients with scarring alopecia or those not responding to initial treatment should be referred to a dermatologist for specialized evaluation 3.