What is the primary feature of drug-induced systemic lupus erythematosus?

The primary feature of drug-induced systemic lupus erythematosus (SLE) is the presence of antihistone antibodies. Drug-induced SLE is a condition resembling classic lupus that can occur due to certain medications, with the most commonly associated drugs being procainamide, hydralazine, isoniazid, and others.

Antihistone antibodies are specific to drug-induced lupus and are distinct from the antibodies typically found in idiopathic SLE, such as anti-dsDNA and anti-Smith antibodies. The presence of antihistone antibodies helps differentiate drug-induced SLE from other forms of lupus and is a key diagnostic marker that clinicians look for in patients presenting with symptoms consistent with lupus following drug exposure.

Other conditions mentioned, such as necrotizing vasculitis, pemphigus vulgaris, and portal hypertension, do not relate specifically to drug-induced SLE. Necrotizing vasculitis refers to inflammation of blood vessels leading to tissue necrosis, which is not a hallmark of drug-induced lupus. Pemphigus vulgaris is an autoimmune blistering disorder that is unrelated to lupus. Portal hypertension is related to liver disease and is not associated with SLE. Hence, antihistone antibodies serve as the defining characteristic of