CASE #2: Bullous pemphigoid
For centuries, bullous pemphigoid (BP) was grouped with and considered a condition similar to pemphigus vulgaris (PV). In 1953, however, Lever recognized BP as a disorder distinct from PV.9 BP, the most common autoimmune bullous dermatosis,10 is generally considered a disease of the elderly; its median age of onset is 60-75 years.11 BP has a higher predominance in men than women; the incidence of BP increases with age.
The etiology of BP can be traced to circulating autoantibodies directed at the basement membrane zone of the skin,12 specifically BP antigens 1 and 2, components of the hemidesmosome adhesion complex. Damage to this complex by a humoral and cellular immune response results in dysadhesion and subepidermal bullae formation.
Clinically, BP manifests as a tense blister with clear fluid on normal to erythematous skin. After rupturing, the blisters may leave an erosion and crust. The oral cavity is involved in only 10%-30% of patients.13 Half of affected patients may also have a peripheral blood eosinophilia.14 Less commonly, BP may present without bullae, as a nonspecific pruritic urticarial eruption.
BP may also be triggered by certain medications.15 Those most commonly implicated include diuretics (e.g., furosemide), penicillamine, captopril, potassium iodide, and some antibiotics.
Skin biopsy of bullous lesions under light microscopy will show a subepidermal blister with an inflammatory infiltrate composed of eosinophils and mononuclear cells in the upper dermis. The bulla cavity may show a variable inflammatory infiltrate with eosinophils and neutrophils. DIF microscopy should be performed on biopsy specimens of perilesional, uninvolved skin in any patient suspected of having BP. Such examination will classically show linear deposits of IgG and C3 along the epidermal basement membrane.
The differential diagnoses of BP include such vesiculobullous disorders as epidermolysis bullosa, dermatitis herpetiformis, PV, and linear IgA bullous dermatoses. In patients with liver disease and bullae on sun-exposed areas, porphyria cutanea tarda (PCT) is also a possibility; PCT can be ruled out with a 24-hour urine porphyrin screen. Other bullous eruptions, including allergic contact dermatitis, bullous impetigo, bullous drug eruptions, and even Stevens-Johnson syndrome, should also be considered.
The mainstay of treatment for generalized BP is corticosteroids. BP can usually be effectively controlled within a couple of weeks by using oral prednisone in doses of 0.5-1.0 mg/kg/day. Because corticosteroids are associated with infection, hyperglycemia, cataracts, and osteoporosis, especially with long-term use, these agents should be gradually tapered. Other immunosuppressive medications, such as azathioprine, methotrexate, cyclosporine, cyclophosphamide, and mycophenolate mofetil, have been used, but they are generally reserved for second-line therapies in patients who do not respond well to corticosteroids.
Although BP is a chronic disease with significant morbidity, most patients achieve clinical remission with treatment. A recent retrospective cohort analysis showed that the mortality of patients with BP is more likely related to advanced age and associated medical conditions than to disease-specific factors.16 This patient’s BP cleared within a month of starting oral prednisone, and he has remained BP-free ever since.
Dr. Chan is a resident in the Department of Dermatology, Baylor College of Medicine, in Houston. He has no relationships to disclose relating to the content of this article.
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