Non-bullous pemphigoid
In some patients, pemphigoid starts off with cutaneous manifestations of BP without bullae, as the only sign of the disease. Pruritic eczematous, papular, or urticaria-like skin lesions may also persist for weeks to months. Bullous phase
The bullous stage of BP shows vesicles and bulla, appearing on apparently normal or erythematous skin, predominantly at  the flexural aspects of the extremities and the lower trunk. Mucosal lesions, which typically are erosions of the oral mucosa, are present in 10 to 30 percent of patients. Occasionally, the blister fluid becomes blood-tinged. The blisters are tense, about 1–4 cm in diameter, leaving eroded and crusted areas, together with urticarial and infiltrated papules and plaques in an annular or figurate pattern.Homology between bullous pemphigoid antigens in the skin and neuronal antigens in the central nervous system has been proposed as a cause for the observed link between bullous pemphigoid and neurologic disease, along with a genetic predisposition. Patients with bullous pemphigoid usually present with two or more other chronic diseases such as neurological disorders(dementia, Parkinsons disease, or stroke). However, further studies are necessary to explore the relationship between these disorders. Cause
The pathogenetic mechanism of blister formation is known, the trigger to the formation of the antibodies to the hemidesmosome antigens is still unknown. Most of the bullous pemphigoid cases are due to autoantibodies (mostly IgG) directed at antigens (BP180 and BP230) arranged at the dermal-epidermal junction.
However, most commonly, drug can be one of the cause of bullous pemphigoid, such as thiazide diuretics, antibiotics (e.g., penicillins, vancomycin), nonsteroidal anti-inflammatory drugs (NSAIDs) and angiotensin-converting enzyme (ACE) inhibitors (e.g., captopril) and possibly angiotensin receptor blockers (ARBs, e.g., valsartan).The implicated drugs include penicillin derivatives, sulfasalazine, ibuprofen, phenacetin, enalapril, captopril, lisinopril, gabapentin, novoscabin, levobunolol ophthalmic solution, tetracoq, influenza, tetanus, and other vaccinations, a homeopathy regimen, nifedipine, 5-aminosalicylic acid, doxazosin, serratiopeptidase, losartan, cephalexin, bumetanide, fluoxetine, chloroquine, antipsychotic drugs, enoxaparin, ciprofloxacin, furosemide (frusemide), neuroleptics, penicillamine, gliptin plus metformin, intravenous iodine, etanercept, levofloxacin, and topical fluorouracil. Influenza vaccination does not appear to be an important trigger for bullous pemphigoid. Trauma, burns, lymphedema, phototherapy, and radiation have been implicated in a very small number of cases. Pathophysiology
The pathophysiology of bullous pemphigoid consists of two major components, which are immunologic and inflammatory. In the immunologic component, autoantibodies act against the hemidesmosomal bullous pemphigoid antigens BP230 (BPAg1) and BP 180(BPAg2 or type XVII collagen) which are located at the lamina lucida of the basement membrane zone. These antigens play an important role in the adhesion complexes that promote epithelial-stromal adhesion. The predominant subclass of antibodies that acts against the antigens is IgG4. IgG1 and IgG2 antibodies are less frequently detected compared to IgG4 antibodies, while IgG3 antibodies are usually absent. When the autoantibodies bind specifically to the target antigens, the complement system and mast cells are activated, thereby representing the inflammatory component. Inflammatory cells such as neutrophils and eosinophils are then attracted to the affected area.