Differentials
Insect or spider bite
SIGNS / SYMPTOMS
Other arthropod assaults may be difficult to differentiate and are the primary consideration in the differential diagnosis.
Fleas and chiggers: usually lower legs.
Mosquitoes: patient is aware of bite.
INVESTIGATIONS
Clinical diagnosis.
Urticaria
SIGNS / SYMPTOMS
Patients may have a history of previous urticaria and/or recent exposure to triggers (e.g., drug or food).
Lesions of urticaria due to other causes tend to be more blanchable and of shorter duration than urticarial bed bug bites
INVESTIGATIONS
Clinical diagnosis.
Scabies
SIGNS / SYMPTOMS
History of exposure to another individual with scabies.
Presents as eczematous papules and patches; some lesions may become nodular; keratotic thickening can be seen on the hands.
Sites of predilection are the interdigital spaces, umbilicus, groin, and axillae.
Burrows (intact tunnel with a tiny dark dot, the mite, at the end) may be seen in the interdigital web spaces.
INVESTIGATIONS
Skin scraping may reveal scabies mites, eggs, and scybala (faeces) on microscopic examination.
Dermatitis herpetiformis
SIGNS / SYMPTOMS
History of coeliac disease (90% of patients).
A recurrent, extremely pruritic condition; typically presents with grouped (herpetiform) erythematous papules, vesicles, and excoriations distributed symmetrically on the chest, elbows, knees, lower back, and buttocks.
INVESTIGATIONS
Skin biopsy shows papillary neutrophilic collections and subepidermal blisters. Direct immunofluorescence shows IgA in the upper dermis arranged in a granular pattern within dermal papillae.[29]
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