Scabies Rash Characteristics
The scabies rash consists of pruritic papules, vesicles, and excoriations in characteristic locations, with pathognomonic burrows (linear tracks up to 1 cm long) being the definitive diagnostic sign, accompanied by intense nocturnal itching that is often out of proportion to visible skin findings. 1, 2
Classic Rash Features
Primary Lesions
- Burrows: Pathognomonic linear tracks, typically up to 1 cm in length, representing the mite's tunneling through the epidermis 1, 3
- Papules: Erythematous, pruritic papules scattered across affected areas 4, 5
- Vesicles: Small fluid-filled lesions that may develop 1, 4
- Excoriations: Secondary scratch marks from intense itching 4, 3
Distribution Pattern
The rash affects specific body regions in adults, sparing the head 2, 3:
- Finger and toe web spaces (most common site for burrows) 4, 3
- Volar wrists and ankles 4, 5
- Axillary folds 1, 5
- Abdomen and buttocks 4, 5
- Male genitalia 4, 5
- Inframammary folds and areolae in women 4, 5
In infants and young children, the scalp and face may be involved, unlike adults 1, 6
Associated Symptoms
Pruritus Characteristics
- Intense nocturnal itching is the hallmark feature, often appearing disproportionate to visible skin changes 2, 3
- With first infestation, itching may take several weeks to develop due to delayed hypersensitivity 2
- With reinfestations, itching can occur within 24 hours due to prior sensitization 2
Inflammatory Changes
- Erythematous macules and plaques with excoriation from scratching 3
- Inflammatory changes particularly prominent in intertriginous areas 2
- Edema and erythema commonly accompany the infestation 7
Atypical Presentations
Crusted (Norwegian) Scabies
- Dry, scaly, hyperkeratotic, and crusted skin, particularly on extremities 3
- Pruritus may be minimal or absent in this variant 2, 3
- Occurs in debilitated, elderly, or immunocompromised patients 1, 2
- Extremely high mite burden makes this form highly contagious 1
Bullous Scabies
- Presents with pruritic blisters and urticarial plaques 8
- Can masquerade clinically, pathologically, and immunologically as bullous pemphigoid 8
- Represents an atypical clinical variant that mimics non-parasitic dermatoses 8
Atypical Presentations in Elderly/Debilitated
- Burrows and pruritus may be absent, with only hyperkeratosis, papules, or vesicles present 1
- Minimal or absent inflammatory changes 2
- Clinical presentation can be highly atypical in nursing home residents 2
Post-Treatment Rash Persistence
A critical pitfall to avoid: Rash and pruritus commonly persist for up to 2 weeks after successful treatment—this is NOT treatment failure and does NOT indicate need for retreatment 1, 6
- In clinical trials, approximately 75% of patients with persistent pruritus at 2 weeks had complete resolution by 4 weeks 7
- Treatment with permethrin may temporarily exacerbate pruritus, edema, and erythema 7
- Retreatment is indicated only if symptoms persist beyond 2 weeks AND living mites are demonstrated 1, 6
Treatment of the Rash
First-Line Therapy
Permethrin 5% cream is the gold standard treatment 1, 6:
- Applied from neck down (including scalp in infants) for 8-14 hours, then washed off 1, 6
- One application is generally curative 1, 6
- Must include under nails, all body folds, and up to edge of all orifices 1
Alternative Therapy
Oral ivermectin 200 μg/kg, repeated in 2 weeks 1, 6:
- Should be taken with food to increase bioavailability 1
- Not recommended for children weighing less than 15 kg or infants under 2 months 6
- Especially useful in institutional outbreaks and crusted scabies 4
Crusted Scabies Requires Combination Therapy
- Topical 5% permethrin cream applied daily for 7 days then twice weekly 1
- PLUS oral ivermectin 200 μg/kg on days 1,2,8,9, and 15 1, 6