Alopecia Areata

Detailed Overview

Alopecia areata is highly unpredictable. It typically presents as round, smooth patches of total hair loss on the scalp or beard, without any scaling or inflammation visible on the skin surface. The disease can remain localized, progress to total loss of scalp hair (Alopecia Totalis), or result in the loss of all body hair (Alopecia Universalis). While the hair follicles are attacked, their stem cells are not destroyed, meaning hair regrowth is always possible, even after years of disease. Psychological impact is profound.

Epidemiology & Demographics

Lifetime risk is approximately 2% in the general population. Occurs at any age, but onset is most common before age 30. Equal incidence in males and females. Affects all ethnicities equally.

Etiological Mechanism

Considered a polygenic autoimmune disease triggered by environmental factors. It is mediated by cytotoxic CD8+ T-cells targeting autoantigens in the anagen-phase hair follicle, collapsing the follicle's immune privilege.

Primary Causes

Autoimmune attack of the hair follicle

Genetic predisposition (HLA class II alleles)

Severe acute emotional or physical stress (potential trigger)

Viral infections (potential trigger)

• Family History: 10-20% of patients have a family history of alopecia areata.
• Concurrent Autoimmune Disease: Increased risk if the patient has Autoimmune Thyroiditis, Vitiligo, or Type 1 Diabetes.
• Atopy: Personal or family history of asthma, eczema, or allergic rhinitis is associated with more severe, recalcitrant disease.

Normal anagen (growing) hair follicles reside in an 'immune-privileged' environment, devoid of MHC class I expression. In alopecia areata, stress signals (like IFN-gamma) induce ectopic expression of MHC class I and II on the follicular epithelium. Autoreactive CD8+ NKG2D+ T-cells recognize follicular autoantigens and release pro-inflammatory cytokines (IFN-gamma, IL-15). This inflammatory swarm (peribulbar lymphocytic infiltrate or 'swarm of bees') arrests hair synthesis, forces the follicle into early catagen, and sheds the hair shaft. Because the bulge region containing follicular stem cells is spared, permanent scarring does not occur.

Characteristic Clinical Presentation

• Sudden hair loss: Rapid appearance of one or more round/oval bald patches, usually noticed by a hairdresser or family member.
• Nail changes: Roughness or pitting of the fingernails may occur before or during hair loss.
• Mild pruritus/burning: Some patients feel a tingling or burning sensation in the area right before hair falls out.

Physical Examination Signs

• Smooth, completely bald, well-demarcated patches with normal-appearing skin (no erythema or scaling).
• Exclamation mark hairs (short, broken hairs measuring 2-3 mm that taper at the base, found at the margin of active patches).
• Positive hair pull test at the periphery of the patch (indicates active disease).
• Nail pitting (fine, pinpoint indentations on the nail plate) or trachyonychia (sandpaper nails).

• Psychosocial distress: High rates of severe anxiety, depression, and social phobia due to altered body image.
• Loss of protective hair functions: Loss of eyelashes/eyebrows causes ocular irritation; loss of nasal hair increases respiratory irritation.

Diagnostic Criteria & Guidelines

Clinical diagnosis based on the classic appearance of non-scarring patchy hair loss and exclamation mark hairs on dermoscopy. Scalp biopsy (showing peribulbar lymphocytic infiltrates) is rarely needed unless diagnosis is in doubt.

Differential Diagnosis

• Tinea Capitis (fungal infection, usually scaly and inflamed)
• Trichotillomania (hair-pulling disorder, hairs broken at different lengths)
• Telogen Effluvium (diffuse thinning, not patches)
• Secondary Syphilis ('moth-eaten' alopecia)

Laboratory Tests & Biomarkers

• TSH and Free T4: Checked to rule out associated autoimmune thyroid disease (Hashimoto's), which is present in up to 25% of patients.
• RPR/VDRL: To rule out syphilis if the presentation is atypical ('moth-eaten').

Imaging Modalities & Findings

• Trichoscopy (Dermoscopy of scalp): Shows yellow dots (keratinized material in empty follicular ostia), black dots (pigmented hairs broken at scalp level), and exclamation mark hairs.

• Patchy Alopecia
  One or multiple distinct patches of hair loss on the scalp or body.
• Alopecia Totalis
  Complete or nearly complete loss of all hair on the scalp.
• Alopecia Universalis
  Complete loss of all hair on the scalp, face (eyebrows/lashes), and entire body.

Second-Line & Adjunctive Therapy

For extensive disease (Totalis/Universalis): Oral JAK inhibitors (Baricitinib 2-4 mg daily or Ritlecitinib 50 mg daily). Alternative: Topical immunotherapy (DPCP or SADBE) to induce a localized allergic contact dermatitis that distracts the immune system.

Surgical & Procedural Management

Hair transplantation is contraindicated and ineffective, as the immune system will attack the transplanted follicles.

Recommended Lifestyle Changes

• Use sunscreen on the exposed scalp to prevent sunburn and skin cancer.
• Wear hats, scarves, or wigs to manage cosmetic concerns and provide environmental protection.
• Use artificial eyelashes or protective eyewear if eyelashes are lost.

Patient Counseling & Advice

Reassure the patient that their overall physical health is not in danger and that the hair follicles remain alive, meaning hair can regrow at any time. However, be honest about the unpredictable nature of the disease: spontaneous remission is common in patchy disease, but relapses are frequent, and extensive disease is harder to treat.

Follow-Up & Monitoring Schedule

Monitor treatment response every 6-8 weeks. Monitor for side effects of intralesional steroids (skin atrophy, hypopigmentation). For patients on JAK inhibitors, monitor CBC, lipid panels, and liver function tests regularly.

Preventive Strategies

No known preventative measures. Stress management techniques may be helpful, though stress is a trigger rather than the root cause.

Highly variable. 50% of patients with mild patchy disease experience spontaneous regrowth within 1 year without treatment. However, 10-20% progress to Totalis or Universalis, where spontaneous recovery is rare (<10%). Poor prognostic factors include onset in childhood, presence of nail disease, and concurrent atopy.