What is the appropriate diagnosis and treatment for a 36-year-old man presenting with a 4-week history of a generalized, intensely pruritic rash with excoriated papules and vesicles on his wrists, fingers, arms, and buttocks?

Diagnosis: Scabies

This clinical presentation is classic for scabies infestation, and the patient should be treated immediately with topical permethrin 5% cream applied from neck to toes, left on overnight (8-14 hours), then washed off, with a repeat application in 7 days.

Clinical Reasoning

The constellation of findings strongly points to scabies:

• Intensely pruritic rash for 4 weeks with characteristic distribution on wrists, interdigital spaces (sides of fingers), arms, and buttocks represents the classic pattern of Sarcoptes scabiei infestation 1
• Excoriated papules and vesicles are pathognomonic for scabies, resulting from the itch-scratch cycle triggered by mite burrowing and hypersensitivity reactions 1
• Distribution pattern involving wrists, finger webs, and buttocks is highly specific for scabies, as these are preferred sites for mite infestation 1
• Duration of 4 weeks is consistent with the typical presentation timeline, as pruritus intensifies after initial sensitization 1

Differential Diagnosis Considerations

While the presentation is characteristic of scabies, other conditions must be briefly considered:

• Atopic dermatitis typically has a more chronic relapsing course and involves flexural areas rather than wrists and finger webs 2, 3
• Contact dermatitis would have visible borders corresponding to allergen exposure and would resolve with avoidance 4, 5
• Drug-induced pruritus should be ruled out by reviewing all medications, including over-the-counter and herbal remedies 1

Diagnostic Workup

Confirm the diagnosis through:

• Skin scraping with microscopy to identify mites, eggs, or fecal pellets (scybala) - this is the gold standard diagnostic test 1
• Dermoscopy can visualize burrows and the "delta wing sign" if available 1
• Examination of close contacts for similar symptoms, as scabies is highly contagious 1

Treatment Protocol

First-Line Treatment

Topical permethrin 5% cream:

• Apply from neck down to entire body surface, including under fingernails 1
• Leave on for 8-14 hours (overnight application) 1
• Repeat application in 7 days to kill newly hatched mites 1
• Treat all household members and close contacts simultaneously, even if asymptomatic 1

Symptomatic Management

For intense pruritus:

• Oral antihistamines (non-sedating preferred) for symptomatic relief during treatment 1
• Topical corticosteroids (triamcinolone 0.1% cream 2-3 times daily) for inflammatory component and excoriated lesions 6, 4
• Emollients liberally to restore skin barrier and reduce xerosis 1, 7

Important Caveats

Post-scabetic pruritus:

• Itching may persist for 2-4 weeks after successful treatment due to residual hypersensitivity reaction 1
• This does NOT indicate treatment failure unless new burrows or lesions appear 1
• Continue symptomatic treatment with topical corticosteroids and antihistamines during this period 1

Environmental measures:

• Wash all clothing, bedding, and towels in hot water (≥60°C) and dry on high heat 1
• Items that cannot be washed should be sealed in plastic bags for 72 hours 1

Treatment Failure Considerations

If symptoms persist beyond 4 weeks post-treatment:

• Consider crusted (Norwegian) scabies in immunocompromised patients, which requires more aggressive treatment 1
• Evaluate for reinfection from untreated contacts 1
• Consider alternative diagnosis if no mites are identified on repeated scrapings 1

Red Flags Requiring Immediate Attention

Rule out severe cutaneous adverse reactions:

• If rash progresses to involve >50% body surface area with systemic symptoms, consider DRESS syndrome or Stevens-Johnson syndrome 8
• Presence of mucosal involvement, skin detachment, or pustules requires immediate hospitalization 1, 8
• These are unlikely in this case given the 4-week stable course, but remain vigilant 8