Medical Archive

Introduction

Scabies

?? 10-15 mites; mild mite burden.

Patients with impaired cell-mediated immunity(eg, HIV) are unable to contain the infection and usually develop crusted scabies (Rt picture).  Associated with thousands or millions of mites.

Symptoms

Rapidly spreading, pruritic rash 
Flexor surfaces of the wrist, lateral surfaces of the fingers and finger webs
Worse at night due to DTH reaction to the mite, mite feces, and mite eggs.
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Erythematous papules and excoriations on the extremities
Linear burrows are the most specific finding.

Diagnosis

Confirmed by skin scrapings from excoriated lesions
Mineral oil test (KOH ??) -> light microscopy

Treatment

Topical Permethrin? TOC. ?? ? ??? ??? ?? ??,  ??? ???. ??? ?? ?!
Lindane (gamma benzene hexachoride) : CNS toxicity? ??? ???? x
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Oral ivermectin:  binds chloride. Ion channels in invertebrate nerve and muscle cells, is an alternate medication for classic scabies and is used with permethrin for crusted scabies.

Permethrine

Inhibits Na channel deactivation -> neuronal membrane depolarization

Malathion

AchEi

Lindane (BHC)

Blocks GABA -> neurotoxicity

Chiggers and other biting mites

Erythematous papules on exposed areas (eg, ankles, waistline)

Tick bites and tick paralysis

Isolated, asymptomatic or pruritic, erythematous papules

• Pathophysiology
  • Tick needs to feed for 4-7 days for the release of neurotoxin
• Clinical presentation
  • Progressive ascending paralysis over hours to days.
  • Paralysis may be localized or more pronounced in 1 leg or arm
  • Sensation is usually normal.
  • No autonomic dysfunction. (cf. GBS)
  • Fever is no present.
  • CSF examination is typically normal (cf. GBS)
• Prognosis
  • Removal usually results in improvement within an hour and complete recovery after several days.

Louse infestation (pediculiasis and pthiriasis)

Blood sucking lice; cause intense pruritus, with associated excoriation
Pediculus capitis: “Head lice”
Pediculus humanus: “Body lice”
Pthirus pubis: “Pubic lice”

Diagnosis

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Treatment

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Permethrin or phenothrin 0.4%, ??/???? 3-4? ??? ??.

Myiasis (fly infestation)

Pentastomiasis

Leech infections

Spider bites

Isolated papule or pustule with localized inflammation.

Brown recluse spider bite

Clinical manifestationss

Over the course of a few days, a deep skin ulcer develops with an erythematous halo and a necrotic center, which can progress to an eschar.

Management

• Cleanse wound & apply ice – The lesion often heals without scarring.
• No surgical débridement until progression of lesion has stopped.
• Supportive management for systemic loxoscelism
• Update tetanus

Black widow spider bite

More pronounced local and systemic manifestations d/t effects of the toxin

Muscle pain (a prominent finding)
Abdominal rigidity (sometimes mimicking a surgical abdomen)
Muscle cramps (seen in >60% of patients)
Wound ulceration is uncommon

Scorpion stings

Hymenoptera stings

Bee and wasp stings

Large local reactions

• Epidemiology & pathophysiology
  • Often d/t bites from Hymenoptera species (eg, bees, ants, wasps)
  • Exaggerated, IgE-mediated, local allergic response (~10% of stung individuals)
  • Associated with possible increased risk for future systemic reactions (<3%-16%)
• Manifestations
  • Significant (~10cm or more) localized swelling, erythema & warmth
  • Swelling & erythema contiguous with site of the sting
  • Develop within 24hr, peak within 24-48hr, resolve in 5-10 days.
• Differential diagnosis
  • Cellulitis
    • Superinfections are uncommon in insect bites
    • Wound generally occur 3-5 days after the initial bite
  • Compartment syndrome
    • Pain out of proportion, paresthesia, and pain with passive stretch. It has been reported but very rare.
• Treatment
  • Cold compresses
  • Oral &/or topical steroids
  • Antihistamines
  • Anti-inflammatory medications
  • Epinephrine autoinjector – debatable.

Stinging ants

Dipteran (fly and mosquito) bites

Flee bites

Hemipteran/heteropteran (true bug) bites

Reduviidae

Bedbugs

Small, red-brown, blood-feeding insects that hide in clusters within the surrounding environment (eg, folds of mattress, cushions) and feed at night.

Clinical manifestations

• 2- to 5-mm, pruritic, erythematous papules in a linear pattern ? “breakfast, lunch, and dinner” bites.
• Central hemorrhagic punctum
• Bites on the palms and soles are uncommon d/t the thickness of the skinl.

Treatment

Supportive
Eradication of bedbugs – insecticides and high heat.

Anti-mite/louse therapy

Centripede bites and millipede dermatitis

Caterpillar stings and dermatitis

Beetle vesication and dermatitis

Delusional infestations