Diagnosis: Bullous arthropod bite reaction
Bullous arthropod bite reaction (BABR) occurs in sensitized individuals as a delayed hypersensitivity immune reaction to insect saliva.1 Patients typically present with grouped localized pruritic or asymptomatic blistering2 and otherwise appear well. Unless secondarily infected, the blisters are non-erythematous and non-purulent, and develop within hours to days of the bite.
Lesion location is key. The distribution and location of the lesions will tip you off to a BABR diagnosis. The lesions in BABR are usually grouped and localized to a specific area of the body, depending on the causative arthropod and the circumstances leading to the bites. For example:
- Lesions caused by Cheyletiella mites are typically found on the forearms, anterior thighs, and lower abdomen after an infested pet sits on an individual’s lap.2,3
- Blisters caused by flea bites are isolated to the lower extremities.4 (We suspect that flea bites were the culprit in our patient’s case.)
- Lesions caused by Cimex lectularius, more commonly known as bedbugs, may be found on the entire body and tend to occur in groups of 3.5
Insect bite? What insect bite?
Most patients will only complain of pruritus and will tell you that they don’t recall having had any insect bites.6 That said, the distribution of the lesions, lack of systemic illness, and otherwise unremarkable physical exam are sufficient for diagnosis.
Occasionally, a punch biopsy with DIF may be necessary to rule out more serious bullous disorders. In BABR, you may see both subepidermal and intraepidermal blistering, with perivascular and interstitial eosinophilic and lymphocytic infiltrates. Blisters separated by strands of keratinocytes create a characteristic multilocular appearance. Unlike autoimmune blistering disorders, DIF is negative in BABR.7 Gram stain, Tzanck smear, bacterial culture, and KOH prep may also provide additional information if infection is a concern.