CHAPTER 67 ■ RASH: VESICULOBULLOUS MARISSA J PERMAN INTRODUCTION Basic to all vesiculobullous (blistering) disorders is the disruption of cellular attachments Blister formation, therefore, follows intracellular degeneration, intercellular edema (spongiosis), or damage to the anchoring structures associated with the basement membrane (hemidesmosomes, basal lamina, anchoring fibrils) The location of these changes can help the physician ascertain a specific diagnosis When histologic information is not readily available or nondefinitive, however, the historical and clinical features of the case must be relied on This chapter will discuss the following entities: infestations, mastocytosis, inherited blistering disorders, acquired autoimmune bullous disorders, friction blisters, and frostbite, as well as the differential and workup for these blistering skin disorders ACQUIRED BLISTERING ERUPTIONS Infestations Insect Bites Insects generally bite exposed skin surfaces Therefore, heaviest involvement occurs on the head, face, and extremities Mosquito bites occur in the warm weather months, whereas flea (Pulex irritans ) bites and bed bug (Cimex lectularius ) bites occur throughout the year Historical information should address contact with pets, recent camping trips or involvement in outdoor activities, and known exposure in close contacts When blisters are present, the more characteristic urticarial papules are usually present in nearby locations, often clustered together or aligned linearly This linear arrangement is often referred to as “breakfast, lunch, and dinner.” The differential includes bullous impetigo, which can easily be ruled out with a Gram stain or bacterial culture In the case of bullous insect bites, the lesions should be negative for bacteria but can occasionally become secondarily infected If there is concern for flea bites, all pets should be evaluated by a professional Bed bugs can be very difficult to locate but may be detected by turning on the lights late at night and inspecting along the mattress seams and legs of the bed Symptomatic treatment for insect bites includes mild to moderate potency topical corticosteroids and antihistamines such as diphenhydramine