Makindo Medical Notes

Related Subjects: |Nikolsky's sign |Koebner phenomenon |Erythema Multiforme |Pyoderma gangrenosum |Erythema Nodosum |Dermatitis Herpetiformis |Lichen Planus |Acanthosis Nigricans |Acne Rosacea |Acne Vulgaris |Alopecia |Vitiligo |Urticaria |Basal Cell Carcinoma |Malignant Melanoma |Squamous Cell Carcinoma |Mycosis Fungoides (Sezary Syndrome) |Xeroderma pigmentosum |Bullous Pemphigoid |Pemphigus Vulgaris |Seborrheic Dermatitis |Pityriasis/Tinea versicolor infections |Pityriasis rosea |Scabies |Dermatomyositis |Toxic Epidermal Necrolysis |Stevens-Johnson Syndrome |Atopic Eczema/Atopic Dermatitis |Psoriasis

🌍 Infestation is common worldwide, affecting all ages, races, and social classes. 🔁 Recurrence usually indicates re-infection rather than treatment failure. Highly contagious in close-contact settings (care homes, hospitals, households).

ℹ️ About

• Scabies = intensely itchy parasitic skin infestation.
• Caused by the mite Sarcoptes scabiei 🪳.
• Commonest in children, elderly, and immunocompromised.

🧬 Aetiology / Pathophysiology

• Type IV delayed hypersensitivity reaction to mite antigens (eggs, faeces).
• Symptoms usually appear ~30 days after infestation.
• Itch = due to immune reaction, not the number of mites (which is usually low).

📡 Spread

• Direct skin-to-skin contact (prolonged, e.g. holding hands, sexual contact).
• Occasionally via shared clothing, towels, bedding.
• 🧑‍⚕️ Norwegian (crusted) scabies: seen in elderly, immunosuppressed → thousands of mites, very contagious.
• Infested person usually carries ~10–12 adult mites; Norwegian scabies = thousands.

⚠️ Risks

• High-risk in crowded institutions: hospitals, nursing homes, childcare settings.
• Spread to sexual partners and household members is common.
• Brief handshakes/hugs usually do not transmit scabies.

🩺 Clinical Features

• Severe itch (worse at night 🌙).
• Common in families: multiple members itchy at same time.
• Rash: excoriated papules, vesicles, pustules; widespread eczema-like rash possible.
• Sites: interdigital spaces, wrists, axillae, waist, genitalia, buttocks, breasts. 👶 Infants/elderly → also scalp, neck, face.
• Burrows: thin, silver-grey lines with a dark dot (mite) at end.
• Secondary infection (impetigo) may complicate severe scratching.

⚖️ Differentials

• Eczema/dermatitis
• Psoriasis
• Bed bug bites or flea bites

🔎 Investigations

• Usually clinical diagnosis.
• Skin scrapings under microscope → mites, eggs, faecal pellets.
• Dermoscopy may help identify burrows.

💊 Management (UK)

• ✅ Treat all close contacts simultaneously (family, partners, carers) regardless of symptoms.
• 🧴 First-line: Permethrin 5% cream (whole body, including scalp/face in children). Leave 8–12 hrs.
• Alternative: Malathion 0.5% lotion if permethrin unsuitable.
• 💡 Reapply after washing hands or body during treatment period.
• Repeat after 7 days to kill newly hatched mites.
• 🧺 Clothes/bedding: wash >50°C. Non-washables → bag for ≥1 week or freeze.
• Resistant/severe cases: oral ivermectin or benzyl benzoate.
• Consider referral to GUM if sexually acquired.

📚 Key Notes

• Pruritus may persist for 2–3 weeks post-treatment (post-scabetic itch) despite cure.
• Crusted scabies = dermatology/infectious diseases emergency (requires oral + topical treatment, isolation).
• School/nursery exclusion: return allowed after 1st treatment (UK guidance).

🎯 Exam Pearls

• Itch worse at night 🌙 = classic clue.
• Burrows in interdigital spaces = pathognomonic.
• Crusted scabies = highly contagious, immunocompromised patients.
• Persistent itch ≠ treatment failure; often hypersensitivity reaction remains.