Probable Diagnosis: SCABIES (Sarcoptes scabiei var. hominis)

Why This Diagnosis Fits Perfectly

The Causative Agent

Clinical Findings in Detail

Symptoms

• Intense, primarily NOCTURNAL pruritus - the hallmark symptom
• Onset: insidious, typically 4-6 weeks after first infestation (sensitization period); with re-infestation, symptoms appear within 2-3 days
• Some patients remain asymptomatic ("carriers") despite harboring mites

Characteristic Lesion Distribution (Predilection Sites)

Skin Lesions

1. Burrows - pathognomonic, short (5-15 mm) thread-like, slightly raised, grayish-white or skin-colored tracks in the epidermis
2. Papules and vesicles - erythematous, excoriated
3. Excoriations - from intense scratching
4. Eczematous dermatitis - secondary to hypersensitivity

Clinical Images

Diagnosis Confirmation

1. Intense nocturnal pruritus
2. Characteristic distribution
3. Epidemiologic link (household contact history)

• Skin scraping - scrape a burrow with a scalpel, place in mineral oil on a slide; microscopy reveals mites (330-450 µm female), eggs, or fecal pellets (scybala) - definitive but low sensitivity
• Dermatoscopy (epiluminescence microscopy) - identifies the "delta-wing jet" sign (mite parts/air bubbles in the stratum corneum); better sensitivity, non-invasive
• KOH mount or cyanoacrylate adhesive strip preparation
• PCR of skin swabs - highest sensitivity, but not routine
• Harrison's Principles of Internal Medicine 22E (2025)

Differential Diagnosis

• Fitzpatrick's Dermatology, Table 178-1

Complications

• Secondary bacterial infection (impetiginization) - most common; can lead to post-streptococcal glomerulonephritis from Streptococcus pyogenes
• Lymphangitis, septicemia - with crusted scabies
• Bullous pemphigoid - scabies can trigger this autoimmune blistering disorder

Treatment in Detail

FIRST-LINE TREATMENT

Permethrin 5% Cream (Drug of Choice)

For crusted (Norwegian) scabies: apply daily for 7 days, then twice weekly until cured

Oral Ivermectin (Alternative / Adjunct)

• Red Book 2021 (Committee on Infectious Diseases); Harrison's 22E

SECOND-LINE / ALTERNATIVE AGENTS

TREATMENT OF CRUSTED (NORWEGIAN) SCABIES

1. Pre-treatment: Apply 6% salicylic acid (keratolytic) to debulk crusts
2. Permethrin 5%: Apply to entire body including scalp, face, and ears
3. Oral ivermectin: 200 µg/kg - give 3-7 doses over 8-30 days
4. Combination of both topical + oral is recommended
5. Isolate the patient during treatment

ANTIPRURITIC / SYMPTOMATIC RELIEF

• Oral antihistamines: Chlorpheniramine (sedating - helps nocturnal itch), cetirizine, or hydroxyzine
• Calamine lotion: Topical soothing/antipruritic
• Menthol/methyl salicylate preparations: Topical relief
• Topical corticosteroids: To calm post-treatment persistent itch ("postscabetic itch") - only after scabicidal treatment
• Emollients: For skin barrier support

Important patient counseling: Even after successful treatment, pruritus and rash can persist for up to 4 weeks due to the ongoing hypersensitivity reaction to dead mites and their debris. This is called "postscabetic itch" and does not mean treatment has failed. Do NOT over-retreat with permethrin as it can cause irritant contact dermatitis.

ENVIRONMENTAL / FOMITE CONTROL (Mandatory)

• Wash all clothing and bedding in hot water (>60°C) and dry on high heat, or heat-press
• Items that cannot be washed: seal in a plastic bag for at least 72 hours (mites die off-host within 2-3 days for normal scabies)
• Clean mattresses, furniture, and upholstered surfaces
• Vacuum carpets and floors

CONTACT TRACING AND SIMULTANEOUS TREATMENT

All household members and close physical contacts must be treated simultaneously, even if asymptomatic.

• Fitzpatrick's Dermatology; Red Book 2021

Summary Treatment Algorithm for This 60-Year-Old Male

STEP 1: Confirm diagnosis (clinical ± dermoscopy/scraping)
         ↓
STEP 2: Permethrin 5% cream - apply neck-to-toe overnight
         Repeat in 7 days
         ↓
STEP 3: Treat ALL household contacts simultaneously (Day 0 and Day 7)
         ↓
STEP 4: Environmental decontamination (laundry, bagging)
         ↓
STEP 5: Antihistamines for itch relief
         ↓
STEP 6: Reassure patient - itch may persist 2-4 weeks post-treatment
         Topical steroid if postscabetic itch is severe
         ↓
If treatment failure → Oral ivermectin 200 µg/kg × 2 doses (Day 1 and Day 14)

Updated Diagnosis Based on Clinical Images + History

What the Images Actually Show

Revised Diagnosis: PRURIGO NODULARIS (with superimposed secondary changes)

• Intensely pruritic, hyperkeratotic, lichenified nodules and plaques
• Predilection for extensor surfaces (elbows, tibial surfaces), waist, inner thighs, back
• Severe "elephant skin" appearance on the knee/tibial region (Image 2)
• Diffuse lichenification across multiple body surfaces

Differential Diagnosis (Ranked by Probability)

Workup Required

1. Skin scraping with KOH + mineral oil microscopy - rule out crusted scabies (mite/egg identification)
2. Tzanck smear from back vesicles - look for multinucleated giant cells (HSV/VZV)
3. VZV PCR or DFA from vesicle fluid - confirm zoster
4. Skin biopsy (from a nodule/lichenified plaque) - confirm prurigo nodularis histology (eosinophilic infiltrate, neural hyperplasia, pseudoepitheliomatous hyperplasia)
5. Full blood count - eosinophilia supports atopic/parasitic etiology
6. Fasting blood glucose + HbA1c - acanthosis-like changes at waist suggest insulin resistance/diabetes
7. Liver function tests, renal function, thyroid function - systemic causes of pruritus
8. HIV serology - consider in severe/atypical presentations
9. Serum IgE - elevated in atopic states

Detailed Treatment Plan

STEP 1: Treat the Acute Zoster on the Back (URGENT - IF CONFIRMED)

• Start antivirals within 72 hours of vesicle onset - delays beyond this reduce efficacy
• Add oral analgesic (paracetamol/tramadol) for pain
• If ear pinna involved with vesicles + facial palsy/vertigo → suspect Ramsay Hunt syndrome → needs IV acyclovir + oral prednisolone + ENT referral

STEP 2: Treat Prurigo Nodularis (Long-term Management)

A. Breaking the Itch-Scratch Cycle (First Priority)

B. Topical Treatment

C. Intralesional Treatment (for individual resistant nodules)

• Intralesional triamcinolone acetonide 10-40 mg/mL injected directly into indurated nodules - highly effective

D. Systemic Treatment for Moderate-Severe Prurigo Nodularis

E. Phototherapy

• Narrowband UVB (NB-UVB) - 3x/week for 8-12 weeks - effective for widespread prurigo nodularis
• PUVA - for refractory disease
• Mechanism: immunomodulation and reduction of itch-mediating nerve fibers

STEP 3: Treat the Lichenification (Post-Inflammatory Skin Changes)

• High-potency topical steroids under occlusion to flatten lichenified plaques
• Coal tar preparations (1-5%) - antipruritic, anti-inflammatory, antiproliferative
• Salicylic acid 5-10% in a base - keratolytic for thick hyperkeratotic plaques (like the severe tibial changes)
• Barrier repair emollients applied liberally 2-3 times daily

STEP 4: Investigate and Treat Underlying Cause

• Diabetes mellitus (waist acanthosis-like changes) - control blood sugar
• Renal failure - treat underlying CKD
• Liver disease - hepatic pruritus
• Hypothyroidism
• Lymphoma/internal malignancy - rule out in a 60-year-old
• Atopic dermatitis - requires specific management
• Psychiatric comorbidity (anxiety/depression) - address with SSRI/referral

STEP 5: Environmental and Lifestyle Measures

• Keep nails short and clean to minimize skin damage from scratching
• Apply ice packs or cold compresses to pruritic areas instead of scratching
• Wear loose, cotton clothing
• Lukewarm (not hot) baths with colloidal oatmeal or oil additives
• Avoid soap directly on affected areas (use soap-free cleansers)
• Low-irritant laundry detergents
• Address psychological stress with counseling/CBT - stress worsens itch

Summary Algorithm

Urgent (Now):
├── Confirm zoster on back → Start valacyclovir 1g TDS x 7 days
│   └── Check ear for Ramsay Hunt syndrome → ENT referral if present
│
Short-term (1-4 weeks):
├── Hydroxyzine at night + cetirizine daytime (break itch cycle)
├── Clobetasol 0.05% under occlusion on nodules
├── Emollients liberally
├── Investigations: skin scraping, Tzanck, bloods, biopsy
│
Medium-term (1-3 months):
├── Treat underlying cause (diabetes/renal/thyroid)
├── Dupilumab (if confirmed prurigo nodularis)
│   or Gabapentin + Mirtazapine
├── NB-UVB phototherapy
│
Long-term:
└── Intralesional triamcinolone for resistant nodules
    Psychological support/CBT