A 28-year-old woman from Mumbai presents with a 2-week history of sudden onset of numerous small, erythematous papules with fine scale on her trunk and proximal limbs. She had an upper respiratory tract infection 3 weeks ago. On examination, lesions are 3–5 mm in diameter, teardrop-shaped, and scattered over the body. She denies any joint pain. What is the most likely diagnosis and the expected clinical course?

Explanation

## Diagnosis: Guttate Psoriasis **Key Point:** Guttate psoriasis is an acute form of psoriasis characterized by sudden onset of small (< 1 cm), teardrop-shaped papules with fine scale, typically triggered by streptococcal infection (pharyngitis, scarlet fever). It accounts for 2–3% of all psoriasis cases. ### Diagnostic Criteria for Guttate Psoriasis | Feature | Guttate Psoriasis | Clinical Significance | |---------|-------------------|----------------------| | **Onset** | Acute (days to weeks) | Often post-streptococcal (3–4 weeks) | | **Morphology** | Small (3–5 mm), teardrop-shaped papules | Distinguishes from plaque type | | **Scale** | Fine, not silvery | Less prominent than plaque psoriasis | | **Distribution** | Trunk, proximal limbs (centripetal) | Characteristic pattern | | **Systemic symptoms** | Absent | No fever or systemic involvement | | **Trigger** | Streptococcal pharyngitis | History of URTI 3 weeks prior | | **Prognosis** | 50% resolve spontaneously; 10–20% progress to plaque psoriasis | Important for counseling | ### Pathophysiology **High-Yield:** Guttate psoriasis is triggered by: 1. **Streptococcal infection** (Group A Streptococcus most common) 2. **Molecular mimicry** — streptococcal antigens cross-react with skin-homing T cells 3. **Th17-mediated immune response** — IL-17 and IL-23 upregulation 4. **Koebner phenomenon** — trauma-induced lesions at sites of infection or scratching ### Clinical Course ```mermaid flowchart TD A[Guttate Psoriasis Onset]:::outcome --> B{Natural History}:::decision B -->|50%| C[Spontaneous Resolution<br/>within 3-6 months]:::action B -->|10-20%| D[Progression to Plaque Psoriasis<br/>within 1-2 years]:::action B -->|30-40%| E[Chronic Guttate Form<br/>Persistent lesions]:::action C --> F[Complete clearance]:::outcome D --> G[Large plaques on extensor surfaces]:::outcome E --> H[Ongoing management needed]:::action ``` ### Why This Is Guttate Psoriasis 1. **Acute onset** — Sudden appearance 2 weeks ago (typical timing) 2. **Post-streptococcal trigger** — URTI 3 weeks prior (classic trigger) 3. **Morphology** — Small (3–5 mm), teardrop-shaped papules (pathognomonic) 4. **Distribution** — Trunk and proximal limbs (centripetal pattern) 5. **Absence of joint pain** — Rules out psoriatic arthritis 6. **Age and demographics** — Young adult (peak incidence 15–35 years) ### Clinical Pearl **Streptococcal Throat Culture:** In suspected guttate psoriasis, obtain throat culture or rapid strep antigen test. If positive, treat with antibiotics (penicillin V or amoxicillin for 10 days). Eradication of streptococcal infection may prevent progression to chronic psoriasis in some patients. ### Mnemonic: GUTTATE Psoriasis - **G**uttate (small, teardrop-shaped) - **U**pper respiratory infection (streptococcal trigger) - **T**runk and proximal limbs (distribution) - **T**eardrop morphology (3–5 mm papules) - **A**cute onset (sudden appearance) - **T**rigger-dependent (post-streptococcal) - **E**ventual course (50% resolve, 10–20% → plaque) ### Differential Diagnosis | Condition | Key Distinguishing Feature | |-----------|---------------------------| | **Pityriasis rosea** | Herald patch, collarette scale, follows Langer's lines, self-limited | | **Secondary syphilis** | Palmoplantar involvement, systemic symptoms (fever, lymphadenopathy), serology positive | | **Viral exanthem** | Monomorphic lesions, rapid resolution (1–2 weeks), no recurrence | | **Guttate psoriasis** | Teardrop papules, post-streptococcal, chronic potential, Auspitz sign | [cite:Fitzpatrick's Dermatology 9e Ch 8]