A 62-year-old man started on an antiarrhythmic agent 8 months ago develops arthralgia, fever, and pleuritic chest pain. ANA is positive at high titre. Anti-dsDNA is negative and complement levels are normal. Which antibody finding best supports the most likely diagnosis?

• A Anti-histone antibodies ✓
• B Anti-ribosomal P antibodies
• C Anti-U1 RNP antibodies
• D Anti-La (SSB) antibodies

Explanation

Procainamide is the classic cause of drug-induced lupus, followed by hydralazine and isoniazid. Anti-histone antibodies are positive in over 95 percent of drug-induced lupus cases, making them the best supportive marker here. The normal complements and negative anti-dsDNA distinguish it from idiopathic SLE. Anti-ribosomal P is specific for idiopathic SLE with neuropsychiatric disease, and anti-U1 RNP defines mixed connective tissue disease.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.