Bullous pemphigoid versus

Bullous pemphigoid is an autoimmune disease that causes the chronic blistering of the skin. It typically has an onset of between 60 and 80 years of age, though it occasionally starts in childhood. It is characterized by blisters that usually develop on a prodromal eruption of urticarial-type skin lesions. Pemphigoid has is most likely to occur on the groin, underarm, abdomen, and especially the lower legs and feet.

Lesions
Lesions tend to be scattered and discreet, with shapes varying from arciform to annular or serpiginous. The rash may be pruritic (itchy), but it is often asymptomatic. The Nikolsky sign, ie, intraepidermal cleavage and slippage resulting from a gentle applied shear force, is typical but not always present. In one study, 4 of 10 patients with bullous pemphigoid had a positive Nikolsky sign at the edge of a blister, but none had the sign on nonblistered skin. Most blisters eventually rupture and form shallow erosions.

Differential diagnosis
The differential diagnosis includes pemphigus vulgaris, which tends to start at 40-60 years of age and which manifests with flaccid blisters on normal skin with a positive Nikolsky sign (in distinction to the tense blisters on urticarial skin seen in bullous pemphigoid). Pemphigus vulgaris is less common but more serious of the 2 conditions. Other blistering conditions that may need to be considered include porphyria cutanea tarda, erythema multiforme, toxic epidermal necrolysis, staphylococcus scalded skin syndrome, and dermatitis herpetiformis.

Cause
The cause of bullous pemphigoid is an unknown autoimmune mechanism wherein autoantibodies attack glycoproteins in the dermal basement membrane. In rare cases, certain drugs may precipitate true disease or may cause a blistering drug eruption, which is a temporary condition that, unlike true pemphigoid, eventually resolves once the offending agent is discontinued.

Furosemide and penicillamine are the classic examples or precipitating agents, but sulfa-based drugs, penicillins, angiotensin-converting enzyme inhibitors, and quinolones have all been implicated. If a pemphigoidlike illness develops soon after exposure to a suspected agent, the drug should be stopped or replaced and a steroid taper initiated. If lesions recur after this, true bullous pemphigoid is likely and consultation with a dermatologist is warranted.

Diagnosis and treatment
The diagnosis of bullous pemphigoid should be confirmed by means of skin biopsy because treatment involves chronic immunosuppression, often for years. Oral steroids are the initial treatment of choice, but other immunosuppressants may help minimize adverse effects of therapy.

A typical starting dosage is prednisone 0.5-1 mg/kg/day. Dosages lower than this are used for mild disease. Topical steroids tend to be as effective as oral agents, but they minimize systemic adverse effects, especially in severe disease. However, oral involvement, increased cost, and difficulty with self-application may limit the use of topical agents in some patients. After the disease is well controlled, a gradual taper to the lowest effective dosing is advisable.