DEFINITION

A pruritic, sterile follicular eruption seen in advanced HIV infection, characterized by eosinophil-rich inflammation centered on hair follicles.

ETIOPATHOGENESIS

• Occurs typically in advanced HIV (low CD4 counts, often <200/µL)

• Mechanism: immune dysregulation → Th2 polarization

  • ↑ IL-4, IL-5 → eosinophil activation and recruitment

• Possible triggers:

  • Reaction to follicular antigens (e.g., Demodex, Malassezia—controversial)

• Not a true infection → sterile process

CLINICAL FEATURES

• Intensely pruritic papules and pustules

• Follicular distribution

• Common sites:

  • Face (especially forehead)

  • Upper trunk

  • Proximal arms

• Lesions may be excoriated due to severe itching

• Chronic, relapsing course

Exam pearl:
Pruritus is often disproportionately severe

HISTOPATHOLOGY

1. FOUNDATIONS (First Principles)

• Hair follicle unit:

  • Infundibulum → upper portion exposed to environment

  • Isthmus and bulb → deeper follicular structures

• Immune cells:

  • Eosinophils → involved in parasitic/allergic responses

  • Release cytotoxic proteins (major basic protein, eosinophil cationic protein)

• Sebaceous gland: lipid-rich environment, potential antigenic site

2. INITIATING EVENT

• Immune dysregulation in HIV → Th2-skewed response

• Leads to eosinophil recruitment around follicles

3. PATHOGENESIS

1. HIV-induced immune imbalance → Th2 dominance

2. ↑ IL-5 → eosinophil proliferation and activation

3. Eosinophils localize to hair follicles

4. Release of cytotoxic granules → follicular damage

5. Inflammation → pruritic papules/pustules

4. HISTOPATHOLOGY

Key feature: folliculocentric eosinophilic infiltrate

• Eosinophils around and within hair follicles

  • Normally absent or minimal

  • Accumulate due to cytokine-driven recruitment

• Follicular spongiosis

  • Edema within follicular epithelium

  • Reflects inflammatory injury

• Eosinophilic microabscesses

  • Collections of eosinophils within follicle

  • Result of intense localized inflammation

• Variable follicular destruction

  • Due to cytotoxic proteins released by eosinophils

• Absence of organisms

  • Important to differentiate from infectious folliculitis

5. TEMPORAL EVOLUTION

• Early: Perifollicular eosinophilic infiltrate

• Established: Intrafollicular eosinophils + microabscesses

• Late: Follicular damage ± post-inflammatory changes

6. NAMING LOGIC & TERMINOLOGY

• “Eosinophilic” → predominant eosinophil infiltrate

• “Folliculitis” → inflammation centered on hair follicles

7. STAINING & MARKERS

• H&E:

  • Eosinophils identified by:

    • Bilobed nucleus

    • Bright eosinophilic cytoplasmic granules

• Special stains:

  • PAS, Gram → negative (helps exclude infection)

• Peripheral blood:

  • May show eosinophilia (supportive finding)

8. PATTERN RECOGNITION & DIAGNOSTIC LOGIC

Key pattern:

• Pruritic follicular papules + eosinophils on histology + HIV context

Differentiate from:

• Bacterial folliculitis → neutrophils + organisms

• Acne → comedones + mixed inflammation

• Demodex folliculitis → mites present

• Drug eruption → more diffuse, not folliculocentric

9. CLINICO-PATHOLOGICAL CORRELATION

• Eosinophil-mediated inflammation → intense pruritus

• Follicular involvement → papules/pustules

• Sterile nature → poor response to antibiotics

• Distribution (face/trunk) reflects follicular density

MANAGEMENT

Core principle:

Control inflammation + treat underlying HIV

First-line:

• Antiretroviral therapy (ART)

  • Most effective long-term control (immune restoration)

Symptomatic treatment:

• Topical corticosteroids

• Oral antihistamines (limited but used)

Other options:

• Phototherapy (UVB) → immunomodulation

• Oral indomethacin (anti-inflammatory effect; classic exam point)

• Itraconazole (variable benefit; mechanism unclear)

PROGNOSIS

• Chronic but improves with immune reconstitution (ART)

• May relapse if CD4 count declines

EXAM-FOCUSED INSIGHTS

• Occurs in advanced HIV with low CD4 count

• Eosinophils—not neutrophils → key distinction

• Severe pruritus is hallmark

• Sterile folliculitis

• Improves with ART (most important treatment)

MUST-KNOW QUESTIONS

1. Which cells predominate in HIV-associated eosinophilic folliculitis?
   Eosinophils

2. Typical CD4 count association?
   <200/µL

3. Main symptom?
   Severe pruritus

4. Distribution of lesions?
   Face, upper trunk, arms

5. Is it infectious?
   No (sterile)

6. Key histological feature?
   Eosinophils around hair follicles

7. What cytokine drives eosinophilia?
   IL-5

8. Most important treatment?
   Antiretroviral therapy

9. Why do antibiotics fail?
   No bacterial infection

10. What is seen in blood tests?
    Peripheral eosinophilia (sometimes)

11. Classic additional treatment option?
    Indomethacin

12. Main differential histological cell type in bacterial folliculitis?
    Neutrophils