usually develops within the first week of antibiotic therapy but up to 2 months after starting an anticonvulsant.
before the rash appears, there is usually a prodromal illness of several days duration resembling an upper respiratory tract infection or 'flu-like illness often with fevers, sore throat, cough, sore eyes, myalgias.
an abrupt onset of a tender/painful red skin rash starting on the trunk and extending rapidly over hours to days onto the face and limbs (but rarely affecting the scalp, palms or soles), the maximum extent is usually reached by four days.
the cutaneous involvement differs from EM by involving a greater proportion of the skin, the absence of typical targets and the predominantly axial disposition. The target-like lesions are asymmetrical and made of two concentric zones and purpuric evolution.
flaccid blisters form and then merge to form sheets of skin detachment, exposing red, oozing dermis. The Nikolsky sign is positive.
mucosal involvement is prominent and severe, although not forming actual blisters
the patient becomes very ill, extremely anxious and in considerable pain. In addition to skin/mucosal involvement, other organs may be affected including liver, kidneys, lungs, bone marrow and joints.