Differential Diagnosis of Follicular Papules

Introduction

Follicular papules are lesions centered on or arising from hair follicles. They may represent abnormal keratinization, infection, or follicular neoplasia. Recognition of the follicular localization and associated features guides diagnosis. This chapter covers the major causes of follicular papules from benign conditions like keratosis pilaris to inflammatory and neoplastic processes.

---

35.1 Non-Inflammatory Follicular Keratotic Papules

35.1.1 Keratosis Pilaris (KP)

• Definition: Common follicular keratinization disorder characterized by keratotic follicular papules.
• Epidemiology: Very common (40-50% of population). Often familial. Associated with atopy.
• Pathogenesis: Abnormal keratinization of the follicular infundibulum → Keratin plugs within follicles.
• Clinical Features:
  • Tiny (1-2mm), rough, follicular papules ("chicken skin").
  • Often skin-colored but may have surrounding erythema (keratosis pilaris rubra).
  • Distribution: Outer upper arms, Thighs, Cheeks.
  • Asymptomatic or mildly pruritic.
• Course: Often improves with age.
• Treatment: Emollients, Keratolytics (Salicylic acid, Lactic acid, Urea). Retinoids for resistant cases.

35.1.2 Keratosis Pilaris Rubra Faceii

• Variant: KP with prominent erythema.
• Distribution: Cheeks (lateral face).
• Clinical Features: Erythema with follicular keratotic papules. Often cosmetically distressing.
• Differential: Rosacea (papulopustules, telangiectasias, NO follicular keratosis).

35.1.3 Lichen Spinulosus

• Definition: Grouped follicular keratotic papules with prominent spines.
• Clinical Features:
  • Patches of follicular papules with horny spines (projecting from follicles).
  • Often skin-colored.
• Distribution: Neck, Buttocks, Thighs.
• Demographics: Children and adolescents.
• Course: Usually self-limited.

35.1.4 Phrynoderma (Vitamin A Deficiency)

• Definition: Follicular hyperkeratosis due to Vitamin A deficiency.
• Clinical Features:
  • Large, dry, follicular keratotic papules ("toad skin").
  • Distribution: Extensor surfaces of arms and thighs.
• Associated Features: Night blindness (nyctalopia), Bitot's spots (conjunctival), Xerophthalmia.
• At-Risk: Malnutrition, Malabsorption, Alcoholism.

---

35.2 Inflammatory Follicular Papules

35.2.1 Acne Vulgaris

• Definition: Chronic inflammatory disorder of the pilosebaceous unit.
• Epidemiology: Most common skin disease. Peak incidence in adolescence.
• Pathogenesis: Sebum overproduction + Follicular hyperkeratinization + Cutibacterium acnes proliferation + Inflammation.
• Lesion Types:
  • Non-Inflammatory: Open comedones (blackheads), Closed comedones (whiteheads).
  • Inflammatory: Papules, Pustules, Nodules, Cysts.
• Distribution: Face, Chest, Upper back (sebaceous areas).
• Key Differentiator from Rosacea: Presence of comedones in acne. Rosacea has NO comedones.

35.2.2 Rosacea (Papulopustular Subtype)

• Clinical Features:
  • Central facial erythema with papules and pustules.
  • Telangiectasias.
  • NO COMEDONES.
  • Flushing triggered by heat, spicy food, alcohol.
• Other Subtypes: Erythematotelangiectatic, Phymatous (Rhinophyma), Ocular.
• Demographics: Fair-skinned adults (typically 30-50 years).

35.2.3 Folliculitis (Covered in Ch. 28)

• Bacterial (S. aureus), Gram-negative, Pityrosporum, Eosinophilic.

---

35.3 Follicular Keratotic and Hyperkeratotic Disorders

35.3.1 Pityriasis Rubra Pilaris (PRP)

• Clinical Features:
  • Follicular keratotic papules that coalesce into orange-red plaques.
  • "Islands of sparing".
  • Waxy, orange palmoplantar keratoderma.
• Histology: Alternating ortho- and parakeratosis ("checkerboard" pattern).
• Types: Classic adult (Type I) often self-limiting over 3 years.

35.3.2 Lichen Planopilaris (LPP)

• Definition: Follicular variant of Lichen Planus affecting the scalp causing scarring (cicatricial) alopecia.
• Clinical Features:
  • Perifollicular erythema and scale at the periphery of alopecic patches.
  • Central scarring alopecia (loss of follicular ostia).
  • Pull test: Positive at active margin.
• Subtypes:
  • Classic LPP.
  • Frontal Fibrosing Alopecia (FFA): Band-like recession of frontal and temporal hairline. Common in postmenopausal women. May involve eyebrows.
  • Graham-Little-Piccardi-Lassueur Syndrome: LPP + Non-scarring axillary/pubic hair loss + Follicular keratotic papules on body.
• Histology: Lichenoid interface reaction at the level of the isthmus/infundibulum. Perifollicular fibrosis.
• Treatment: Topical and intralesional steroids. Hydroxychloroquine. Finasteride/Dutasteride for FFA.

35.3.3 Darier Disease (Keratosis Follicularis)

• Definition: Autosomal Dominant genodermatosis affecting keratinization.
• Gene: ATP2A2 (encodes SERCA2 calcium pump).
• Clinical Features:
  • Greasy, warty, yellow-brown keratotic papules.
  • Coalesce into plaques in seborrheic distribution.
  • Distribution: Chest, Back, Scalp, Forehead, Nasolabial folds.
  • Nail Changes: Red and white longitudinal streaks, V-shaped nicking of nail edge.
  • Palmar pits.
  • Mucous membrane involvement: "Cobblestone" papules on palate.
• Aggravating Factors: Heat, Sweating, Sun exposure. Worsens in summer.
• Histology: Dyskeratosis (corps ronds and grains) + Acantholysis (suprabasal clefts).
• Treatment: Topical retinoids, Emollients, Sun protection. Systemic retinoids for severe cases.

35.3.4 Keratosis Pilaris Atrophicans Variants

A group of conditions featuring follicular keratosis with subsequent atrophy and scarring.

• Keratosis Pilaris Atrophicans Faciei (Ulerythema Ophryogenes): Follicular papules on lateral eyebrows → Atrophy → Eyebrow loss.
• Atrophoderma Vermiculatum: Pitted, "worm-eaten" scarring on cheeks. Begins in childhood.
• Keratosis Follicularis Spinulosa Decalvans: Scalp scarring alopecia + Follicular papules on body + Photophobia.

---

35.4 Diagnostic Algorithm

Loading diagram...

---

35.5 Summary Comparison Table

---

35.6 Clinical Pearls

1. Rough papules on outer upper arms → Keratosis pilaris. Common, benign, associated with atopy.
2. Acne has comedones; Rosacea does NOT. This is the key differentiator.
3. Greasy papules in seborrheic areas + V-shaped nail nicking → Darier Disease.
4. Scarring alopecia + Perifollicular scale → Lichen planopilaris. Check for Frontal Fibrosing Alopecia variant.
5. Orange-red plaques + Follicular papules + Islands of sparing → PRP.
6. Eyebrow loss with follicular papules → Ulerythema ophryogenes (KP atrophicans).
7. Follicular papules in malnourished patient → Phrynoderma (Vitamin A deficiency).