Immune-related adverse events

irAEs: Mechanism - Friendly Fire Unleashed

• Immune Checkpoint Inhibitors (ICIs) disrupt the brakes on the immune system, primarily T-cells, leading to an exaggerated anti-tumor response.
• Mechanism: By blocking inhibitory pathways, ICIs promote T-cell activation and proliferation.
  • CTLA-4 Inhibitors (e.g., Ipilimumab): Block the "don't start" signal.
  • PD-1/PD-L1 Inhibitors (e.g., Nivolumab, Pembrolizumab, Atezolizumab): Block the "don't kill" signal on peripheral tissues.
• Pathophysiology: This sustained T-cell activation leads to a loss of self-tolerance. Activated T-cells infiltrate and attack healthy, non-cancerous tissues, causing "off-target" inflammation.

⭐ High-Yield Fact: irAEs can mimic autoimmune diseases and affect any organ system. The skin (dermatitis), colon (colitis), and endocrine glands (hypophysitis, thyroiditis) are most commonly affected.

irAEs: Clinical Spectrum - Organs Under Siege

Immune checkpoint inhibitors can trigger an inflammatory response against various organs, mimicking autoimmune disorders. The timing of onset varies, from days to months after starting therapy.

• Dermatologic (Most Common):

  • Maculopapular rash and pruritus are frequent early signs.
  • Vitiligo-like depigmentation is often associated with a good response in melanoma patients.
  • Severe reactions: Stevens-Johnson syndrome (SJS) / Toxic Epidermal Necrolysis (TEN).

• Gastrointestinal:

  • Colitis presenting as diarrhea (can be watery or bloody), abdominal pain, and cramping.
  • Requires prompt evaluation to rule out infectious causes.

• Endocrinopathies:

  • Hypophysitis: Headache, fatigue, visual changes.
  • Thyroiditis: Can present as hyperthyroidism followed by hypothyroidism.
  • Adrenal insufficiency & Type 1 Diabetes Mellitus.

• Hepatic & Pneumonitis:

  • Hepatitis: Often asymptomatic, detected by ↑ AST/ALT.
  • Pneumonitis: One of the most serious irAEs; presents with cough, dyspnea, chest pain.

⭐ High-Yield Fact: irAEs can manifest weeks, months, or even more than a year after the discontinuation of immunotherapy, requiring a high index of suspicion.

• Musculoskeletal & Neurologic:
  • Myositis, inflammatory arthritis.
  • Rare but severe: Guillain-Barré syndrome, myasthenia gravis.

irAEs: Management - Dousing the Flames

Management hinges on severity, graded by the Common Terminology Criteria for Adverse Events (CTCAE).

• Goal: Mitigate immune-mediated damage while preserving anti-tumor effects.
• Core Principle: Withhold immunotherapy and initiate immunosuppression.

⭐ Exam Favorite: While infliximab is a go-to for steroid-refractory immune-mediated colitis, it is contraindicated in immune-mediated hepatitis due to risk of drug-induced liver injury.

High‑Yield Points - ⚡ Biggest Takeaways

• Immune-related adverse events (irAEs) are inflammatory toxicities from checkpoint inhibitors like anti-CTLA-4 and anti-PD-1/PD-L1 agents.
• The mechanism involves an autoimmune-like, T-cell mediated attack on normal organs.
• Common sites include the skin (dermatitis), GI tract (colitis), liver (hepatitis), and endocrine glands (hypophysitis, thyroiditis).
• Hypophysitis is classically linked to ipilimumab; presents with headache and pituitary dysfunction.
• Pneumonitis is a severe, potentially fatal irAE requiring immediate cessation of therapy.
• Mainstay of treatment is corticosteroids; severity dictates management.