What is the likely diagnosis for a patient with 1mm raised erythematous papules on the genitals and abdomen, accompanied by itchiness, and a partner with similar symptoms on their back?

Likely Diagnosis: Scabies

Based on the clinical presentation of 1mm raised erythematous papules on the genitals and abdomen with itching, affecting both partners in different body locations, scabies is the most likely diagnosis. 1

Clinical Reasoning

The key diagnostic features pointing to scabies include:

• Distribution pattern: Scabies characteristically affects the genitals, abdomen, and back—exactly matching this presentation 1
• Transmission to partner: The fact that a sexual partner has similar itchy lesions on their back strongly suggests a contagious ectoparasitic infection 1, 2
• Pruritus as predominant symptom: Itching is the hallmark of scabies, caused by sensitization to Sarcoptes scabiei 1
• Papular morphology: The 1mm raised erythematous papules are consistent with scabies lesions 1

Why Not Other Diagnoses

Pediculosis pubis (pubic lice) is less likely because:

• Pubic lice typically remain confined to areas with coarse hair (pubic region, occasionally trunk hair) and rarely cause widespread papular eruptions on the abdomen 1, 3
• Patients usually directly observe lice or nits, which wasn't mentioned 2, 3
• The partner's back involvement is atypical for pubic lice 1

Genital herpes is excluded because:

• HSV presents as vesicles that progress to ulcers, not persistent papules 1, 4
• Lesions typically crust and heal within less than 10 days 1, 4
• The 1mm papular morphology doesn't match herpetic vesicles 4

Recommended Treatment

Permethrin 5% cream applied to all areas of the body from the neck down and washed off after 8-14 hours is the first-line treatment 1

Alternative option:

• Lindane 1% lotion or cream (1 oz or 30g) applied thinly to all body areas from neck down, washed off after 8 hours 1
  • Caution: Do not use lindane after bathing, or in patients with extensive dermatitis, pregnant/lactating women, or children under 2 years 1

Critical Management Steps

Partner treatment is mandatory:

• Sex partners within the last month must be treated simultaneously to prevent reinfection 1, 3
• The CDC recommends a 3-month look-back period for partner management 3

Environmental decontamination:

• Machine wash or dry-clean all bedding and clothing, or remove from body contact for at least 72 hours 1
• Use hot water cycles for washing 1
• Fumigation is unnecessary 1

Important Caveats

Persistent pruritus after treatment:

• Itching may continue for several weeks even after successful treatment due to ongoing immune response 1
• Re-treatment after 1 week is recommended only if live mites are observed, not just for persistent symptoms 1

Consider STI screening:

• Since scabies among adults may be sexually transmitted, evaluate both partners for other sexually transmitted infections 1, 2

Follow-up timing:

• Reassess after 1 week if symptoms persist 1
• Retreat with an alternative regimen if not responding to initial treatment 1