**9. Differential diagnosis**

Diagnosis is more difficult in patients with only oral lesions. Differential diagnoses for mucosal lesions include stomatitis secondary to herpes simplex virüs, aphthous ulcers, lichen planus, erythema multiforme, Stevens-Johnson syndrome, paraneoplastic pemphigus cicatricial pemphigoid, autoimmune diseases such as systemic lupus erythematosus or dermatitis herpetiformis [1, 19]. The differential diagnosis of cutaneous lesions includes other forms of pemphigus, bullous pemphigoid, linear Ig A bullous dermatosis, erythema multiforme, Hailey-Hailey disease and Grover's disease, epidermolysis bullosa acquisita [1, 19]. Demonstration of IgG autoantibodies against keratinocyte cell surfaces and anti-Dsg3 IgG will exclude these diseases (except drug-induced pemphigus vulgaris and paraneoplastic pemphigus). Fresh bullous pemphigoid blisters are tense due to a subepidermal division. The Hailey-Hailey disease has full-thickness acantholysis 'dilapidated brick wall' with epidermal hyperplasia and impetiginized scales, and acantholysis does not extend follicles down as in pemphigus. Transient acantholytic dermatosis exhibits only small intraepidermal foci of acantholysis [1].
