A 62-year-old man presents to the emergency department with skin lesions. He felt itchy recently, then noticed skin lesions that broke out prompting him to come to the emergency department. He recently went camping and hiking in the woods. The patient drinks 1-2 beers per day and smokes 1 pack of cigarettes per day. He is currently sexually active with multiple partners and does not use condoms. The patient was discharged 1 week ago for pneumonia which was treated with azithromycin; however, he feels that his symptoms may be returning. His temperature is 99.5°F (37.5°C), blood pressure is 157/78 mmHg, pulse is 90/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam reveals the findings in Figure A on the patient's arm. The skin lesions are thick and do not break when pressure is applied. Which of the following most appropriately describes the most likely diagnosis?
IgG in a fish-net pattern
Type IV hypersensitivity reaction
Linear IgG along the basement membrane
Multi-nucleated giant cells
Linear IgG along the basement membrane
This patient is presenting with pruritic bullous skin lesions with a thick/tough covering suggesting a diagnosis of bullous pemphigoid. Linear IgG binding of anti-hemidesmosome antibodies along the basement membrane is the underlying cause of this disease.

Bullous pemphigoid presents with a urticarial prodrome in elderly patients followed by the formation of tense bullae that do not break when pressure is applied to them. IgG antibodies bind the hemidesmosome along the basement membrane and appear linear on immunofluorescence. Risk factors that are associated with this condition include the initiation of new medications such as loop diuretics, metformin, and neuroleptics. Steroids are the treatment of choice.

Miyamoto et al. review the evidence regarding the diagnosis and treatment of bullous pemphigoid. They discuss how high-potency corticosteroids are the mainstay of treatment for this disease. They recommend considering adjuvant therapy with doxycycline, dapsone, and immunosuppressants.

Figure/Illustration A is a clinical photograph showing bullous skin lesions (red circles). These lesions are tense and do not separate/break when pressure is applied to them and are classically seen in bullous pemphigoid.

Incorrect Answers:
Answer A: IgG in a fish-net pattern suggests a diagnosis of pemphigus vulgaris, which presents with skin lesions that are flaccid and break easily when pressure is applied. Treatment is with corticosteroids.

Answer C: Multi-nucleated giant cells suggests a diagnosis of HSV or herpes zoster virus, which presents with potentially painful vesicles distributed in a dermatomal pattern (for zoster). Treatment is with antivirals such as valacyclovir.

Answer D: Panniculitis suggests a diagnosis of erythema nodosum, which presents with painful, raised nodules that are associated with inflammatory disorders and infection. Treatment is centered on addressing the underlying pathology.

Answer E: Type IV hypersensitivity reaction suggests a diagnosis of contact dermatitis, which presents with pruritic lesions after exposure to a particular antigen such as poison ivy, poison oak, or nickel. Treatment is avoidance of the precipitating agent and steroids as well as symptomatic control.

Bullet Summary:
Bullous pemphigoid occurs secondary to anti-hemidesmosome antibodies which appear linear along the basement membrane on immunofluorescence.