What is the diagnosis and recommended treatment for a patient with generalized nocturnal pruritus and a small papular rash suggestive of scabies?

Diagnosis and Treatment of Suspected Scabies with Nocturnal Pruritus

This presentation is classic for scabies and should be treated immediately with permethrin 5% cream applied from head to toe (including scalp in infants/elderly), left on for 8-14 hours, then washed off—one application is generally curative. 1

Clinical Diagnosis

The combination of generalized nocturnal pruritus with a small papular rash is highly suggestive of scabies and warrants empiric treatment even before confirmatory testing. 2, 3

Key diagnostic features that support scabies:

• Intense nocturnal itching affecting all body regions except the head (in adults) is virtually pathognomonic for scabies 3, 4
• The itch appears out of proportion to visible skin findings, which is characteristic 3
• Small papular rash with excoriations, often with burrows (up to 1 cm linear tracks) on close inspection 2, 3
• Typical distribution: finger webs, wrists, axillary folds, abdomen, buttocks, inframammary folds, and genitalia in men 2
• Scabies affects >200 million individuals annually and is highly contagious through skin-to-skin contact 5

Definitive diagnosis is made by microscopic identification of mites, eggs, or fecal pellets from skin scrapings of burrows, though dermoscopy has become a useful clinical tool. 2, 5

Immediate Treatment Protocol

First-line therapy: Permethrin 5% cream 1, 2, 5

• Apply thoroughly from head to soles of feet (approximately 30 grams for average adult) 1
• In infants and elderly patients, also treat the scalp, temple, and forehead because these areas can be infested 1
• Leave on for 8-14 hours, then wash off with shower or bath 1
• One application is generally curative 1

Permethrin is preferred because it provides greater tolerability due to low inherent toxicity and minimal percutaneous absorption compared to alternatives like lindane. 2

Alternative and Adjunctive Treatments

For treatment failures or special circumstances:

• Oral ivermectin 200 mcg/kg as a single dose is highly effective and well-tolerated 2, 5
• Ivermectin is especially indicated for crusted scabies, immunocompromised hosts, institutional outbreaks, and as prophylaxis for close contacts 2
• Other topical options include benzyl benzoate, precipitated sulfur, and balsam of Peru 5

Critical Management Points

Post-treatment pruritus is common and does NOT indicate treatment failure:

• Patients frequently experience persistent itching after successful treatment due to ongoing hypersensitivity reaction to dead mites 1, 4
• This is rarely a sign of treatment failure and is not an indication for retreatment 1
• Retreatment is only necessary if demonstrable living mites are found after 14 days 1

Symptomatic relief during and after treatment:

• High-lipid emollients applied twice daily as universal first-line symptomatic therapy 6
• Non-sedating antihistamines (fexofenadine 180 mg or loratadine 10 mg daily) for itch relief 6
• Avoid sedating antihistamines long-term due to dementia risk, especially in elderly patients 6, 7

Environmental and Contact Management

Essential measures to prevent reinfestation:

• Treat all close contacts simultaneously, even if asymptomatic, because transmission occurs through skin-to-skin contact 2
• Wash clothing, bedding, and towels in hot water 2
• Items that cannot be washed should be sealed in plastic bags for at least 72 hours 2

When to Refer or Reconsider Diagnosis

Refer to dermatology if: 3

• Diagnostic doubt remains after initial evaluation
• Patient is under 2 months of age
• Lack of response to two courses of different scabicides
• Crusted (Norwegian) scabies is suspected
• History suggests risk of sexually transmitted infection (with pubic lice)

Consider alternative diagnoses if:

• Nocturnal pruritus persists beyond 4 weeks after adequate treatment with no evidence of living mites 1
• Initial workup should still include CBC with ferritin, liver function tests with bile acids, and renal panel because systemic diseases (iron deficiency, cholestatic liver disease, uremia) account for 15-25% of chronic generalized pruritus 6

Common Pitfalls to Avoid

• Do not delay treatment while awaiting confirmatory microscopy if clinical suspicion is high—scabies is a clinical diagnosis 3
• Do not retreat immediately for persistent itch within 14 days post-treatment; this is expected and not treatment failure 1
• Do not forget the scalp in infants, elderly, and immunocompromised patients 1
• Do not treat the patient alone—all household and close contacts require simultaneous treatment 2
• Crusted scabies may not be itchy and presents with hyperkeratotic, crusted skin on extremities—this variant requires oral ivermectin 3, 8