Psoriasiform Dermatitis: Histopathology, Differential Diagnosis, and Management
Psoriasiform dermatitis is a histologic pattern characterized by epidermal hyperplasia (acanthosis), elongated rete ridges, parakeratosis, and neutrophilic infiltrates in the stratum corneum (Munro microabscesses) — resembling psoriasis but not specific to it.
Histologic Hallmarks
- Parakeratosis (retained nuclei in stratum corneum) with neutrophils.
- Regular acanthosis (test-tube shaped rete ridges).
- Suprapapillary thinning, dilated capillaries.
- Absent granular layer.
Differential Diagnosis (Clinical + Histologic Correlation)
| Condition | Distinguishing Features |
|---|---|
| Psoriasis Vulgaris | Classic plaques (scalp, extensor), Auspitz sign, nail pitting, family history. Histology: uniform, prominent microabscesses. |
| Seborrheic Dermatitis | Greasy scale (scalp, face, chest). Histology: less regular acanthosis, shoulder parakeratosis, yeast forms. |
| Nummular / Chronic Eczema | Coin-shaped, very pruritic. Histology: spongiosis + psoriasiform (mixed). |
| Mycosis Fungoides (CTCL) | Poikiloderma, patches/plaques/tumors. Histology: epidermotropism, Pautrier microabscesses (cerebriform nuclei). |
| Pityriasis Rubra Pilaris | Follicular papules, palmoplantar keratoderma, "islands of sparing." Histology: alternating ortho/parakeratosis. |
| Drug Eruption | Temporal link. Histology: eosinophils, interface changes. |
| Tinea (Dermatophytosis) | Annular, scaling border. KOH prep positive. Histology: hyphae in stratum corneum (PAS/GMS). |
Management
- Topical: Corticosteroids (potency by site), vitamin D analogs (calcipotriene), calcineurin inhibitors (tacrolimus), tar, salicylic acid.
- Phototherapy: NB-UVB (first-line for widespread).
- Systemic: Methotrexate, cyclosporine, acitretin, apremilast, biologics (TNF, IL-17, IL-23 inhibitors) — for psoriasis or severe refractory psoriasiform dermatitis.
- Trigger avoidance: Stress, trauma (Koebner), infections, medications (β-blockers, Li, antimalarials).
Biopsy with clinicopathologic correlation is essential for definitive diagnosis and targeted therapy.
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