In a homeless adult with a one‑month history of multiple pruritic, scabbed/excoriated lesions on bilateral lower extremities, likely from insect or spider bites and no purulent drainage, what evaluation steps and treatment options are recommended?

Evaluation and Treatment for Suspected Scabies in a Homeless Patient

This patient most likely has scabies, and you should immediately obtain skin scrapings for microscopy to confirm the diagnosis, then treat empirically with permethrin 5% cream or oral ivermectin 200 mcg/kg while awaiting results, given the classic presentation of persistent pruritus in a homeless individual with excoriated lesions on the lower extremities.

Clinical Reasoning

The constellation of findings—one month of persistent pruritus, homelessness, outdoor sleeping, and excoriated lesions on bilateral lower extremities—strongly suggests scabies rather than simple insect bites. While the patient attributes these to spider/insect bites, true arthropod reactions typically resolve within days to weeks, not persist for a month with ongoing pruritus 1, 2.

Key Diagnostic Features Present:

• Persistent nocturnal pruritus (characteristic of scabies)
• Duration >1 month (insect bites would have resolved)
• High-risk population (homelessness is a major risk factor) 2
• Excoriated lesions (from intense scratching)
• Lower extremity involvement (common scabies distribution)

Immediate Diagnostic Steps

Confirm the Diagnosis:

1. Perform skin scraping with mineral oil from multiple lesions, particularly looking for burrows (though these may be absent in "scabies surrepticius"—the non-classic presentation) 1

2. Look specifically for:

   • Burrows in finger/toe webs, wrists, axillary folds, genitalia (in men), abdomen
   • Papules, vesicles, and excoriations in typical distributions
   • Any hyperkeratotic plaques (would suggest crusted scabies, though less likely without immunocompromise)

3. Microscopy is definitive: Visualization of mites, eggs, or fecal pellets confirms the diagnosis 1, 3

Important Caveat:

Even without microscopic confirmation, you can establish a clinical diagnosis if the patient has pruritus plus classically distributed lesions 1. Given the homeless status and persistent symptoms, empiric treatment is justified while awaiting confirmation.

Treatment Protocol

First-Line Options:

Option 1: Permethrin 5% cream (preferred for classic scabies)

• Apply from neck down to entire body, including under fingernails
• Leave on for 8-14 hours, then wash off
• Repeat application in 7-14 days (essential—single treatment often fails) 1, 3
• Greater margin of safety due to low toxicity and minimal absorption 3

Option 2: Oral ivermectin 200 mcg/kg

• Single dose, repeat in 7-14 days
• Particularly indicated for:
  • Homeless populations (compliance concerns with topical therapy)
  • Potential crusted scabies
  • Difficulty applying topical treatment 3
• May be the most practical choice for this patient given housing instability

Option 3: Combination therapy

• Both permethrin AND ivermectin for severe or treatment-resistant cases 1

Adjunctive Symptomatic Treatment:

Once scabies treatment is initiated:

• Oral antihistamines for pruritus relief
• Topical or oral corticosteroids may be added for severe itching (only AFTER starting scabicide therapy) 1

Critical Management Considerations

Screen for Bacterial Superinfection:

The excoriated lesions place this patient at risk for:

• Impetiginization (Staphylococcus aureus, Streptococcus pyogenes)
• Cellulitis
• Potential systemic complications (sepsis, post-streptococcal glomerulonephritis) 1

If purulent drainage, warmth, or spreading erythema develops: Add systemic antibiotics covering Staph and Strep.

Environmental and Contact Management:

• Treat all close contacts simultaneously (other homeless individuals in same sleeping area) 3
• Wash all clothing and bedding in hot water
• Items that cannot be washed should be sealed in plastic bags for 72 hours 3

Follow-Up Protocol:

Pruritus may persist for 2-4 weeks after successful treatment due to hypersensitivity reaction to dead mites. However, if symptoms persist beyond 4 weeks or worsen:

Consider:

1. Inadequate treatment (most common—ensure second dose was given)
2. Reinfection (untreated contacts)
3. Resistance to therapy (rare but increasing) 1
4. Alternative diagnosis (though less likely given presentation)

Special Alert for This Population:

Homeless patients have higher rates of crusted scabies and treatment failure 2, 4. If you observe any hyperkeratotic plaques or the patient appears immunocompromised, this requires multiple treatments (often 5-7 doses of ivermectin plus daily permethrin for 1-2 weeks) plus keratolytic therapy 1.

What NOT to Do:

• Do not delay treatment waiting for microscopy results in a high-probability case
• Do not give only one treatment dose—recurrence is nearly guaranteed 1
• Do not start corticosteroids before initiating scabicide therapy (will worsen infestation)
• Do not assume "insect bites" when pruritus persists beyond 2-3 weeks

The British guidelines 5 address generalized pruritus without dermatosis, which does not apply here since visible lesions are present. The stinging insect guideline 6 addresses anaphylaxis prevention, not chronic pruritic dermatosis, and is not relevant to this presentation.