## Diagnosis: Crusted (Norwegian) Scabies **Key Point:** Crusted scabies is a severe, highly contagious variant characterized by hyperkeratotic crusts harbouring thousands of mites, occurring predominantly in immunocompromised or debilitated patients. ## Clinical Features Distinguishing Crusted Scabies | Feature | Typical Scabies | Crusted Scabies | |---------|-----------------|------------------| | **Mite burden** | 10–15 mites | Thousands to millions | | **Morphology** | Burrows, papules, nodules | Thick, hyperkeratotic crusts | | **Distribution** | Interdigital spaces, wrists, axillae | Hands, feet, face, trunk, nails | | **Pruritus** | Severe, nocturnal | Variable; may be minimal | | **Risk factors** | Immunocompetent | Immunosuppression, diabetes, leprosy, HIV | | **Contagiousness** | Moderate | Extremely high | | **Response to single permethrin** | Usually curative | Often inadequate | **High-Yield:** This patient's diabetes, widespread crusted lesions, and failure of prior single-application permethrin therapy are classic red flags for crusted scabies. ## Recommended Management ### First-Line: Combination Therapy **Mnemonic:** **CRUST** — **C**rusted scabies needs **R**epeat **U**se of **S**ystemic **T**reatment 1. **Oral Ivermectin** (preferred systemic agent) - Dose: 200 μg/kg on days 1, 2, and 8 - Rationale: Penetrates crusts better than topical agents; kills adult mites and larvae - Repeat dosing: Essential because ivermectin does not reliably kill eggs; day-8 dose targets newly hatched mites 2. **Topical Agent** (concurrent with ivermectin) - Permethrin 5% cream: Apply to entire body, repeat after 7 days - OR Sulfur ointment 10%: More penetrating for thick crusts; apply daily for 5–7 days - Rationale: Topical agents reach mites in superficial crusts; combination maximizes efficacy 3. **Keratolytic Agents** (adjunctive) - Salicylic acid 5–10% or urea ointment to soften crusts and enhance penetration of scabicides ### Post-Treatment Monitoring - Clinical review at 2 weeks; repeat microscopy to confirm mite eradication - Secondary bacterial infection is common; use prophylactic or therapeutic antibiotics as needed - Isolate patient during treatment due to extreme contagiousness **Clinical Pearl:** Crusted scabies can spread to healthcare workers and other patients; strict contact precautions are mandatory during hospitalization. ## Why This Patient Has Crusted Scabies 1. **Immunosuppression:** Poorly controlled diabetes impairs cell-mediated immunity, allowing unchecked mite proliferation. 2. **Prior inadequate treatment:** Single-application permethrin failed to eradicate the infestation, likely because eggs survived. 3. **Progressive disease:** Over 6 months, mite burden escalated from typical to crusted form. 
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