A 55-year-old man started on procainamide for an arrhythmia develops arthralgia, fever, pleuritic chest pain, and a malar rash. ANA is positive. Which finding best supports drug-induced lupus rather than idiopathic SLE?

• A High-titre antibodies against single-stranded DNA
• B Antibodies against double-stranded DNA
• C Low serum complement levels
• D Antibodies against histone complexes ✓

Explanation

Drug-induced lupus is characterised by anti-histone antibodies, present in over 75% of cases, along with a positive ANA and anti-single-stranded DNA. The key discriminator is that anti-dsDNA antibodies and hypocomplementaemia are characteristically absent in drug-induced disease, because immune-complex glomerulonephritis rarely occurs. Procainamide carries the highest risk of any drug, followed by hydralazine. Symptoms usually remit weeks to months after withdrawal of the offending agent.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.