Drug-induced lupus erythematosus

• Epidemiology
  • Most common in individuals 50–70 years of age
• Etiology & Risk Factors
  • Offending Agents (Classic “SHIPP-E” Mnemonic):
    • Sulfa drugs
    • Hydralazine c
    • Isoniazid (INH)
    • Procainamide (Highest risk)
    • Phenytoin
    • Etanercept (and other TNF-α inhibitors)
    • Others: Minocycline, Quinidine, Methyldopa.
  • Risk Factors: Slow acetylators (Phase II metabolism, hepatic N-acetyltransferase deficiency) are at ↑ risk due to accumulation of drug metabolites.
• Pathophysiology
  • Drugs or their metabolites bind to proteins/DNA, creating neoantigens that stimulate an autoimmune response.
  • Often involves genetic susceptibility (e.g., HLA-DR4).
• Clinical features (usually manifest ≥ 1 month after medication initiation)
  • Constitutional: fatigue, fever, and weight loss
  • Musculoskeletal (most common, ~90%): Symmetric, non-erosive polyarthritis or polyarthralgias (similar to idiopathic SLE).
  • Skin lesions (e.g., malar rash)
  • Key High-Yield Negative Findings:
    • No renal involvement (lupus nephritis is exceedingly rare).
    • No CNS involvement (absence of seizures, psychosis, or neuropathy).
• Diagnostics
  • ANAs are positive in nearly all patients.
  • Antihistone antibodies
    • Antihistone antibodies are seen in 90–95% of patients.

Tip

DILE can manifest with various features that are also seen in idiopathic SLE (e.g., fever, arthritis, malar rash, serositis) but typically does not affect the CNS or kidneys, unlike SLE.