Immune checkpoint inhibitors can cause hypophysitis, adrenal insufficiency and thyroiditis, sometimes months into treatment or after it stops. The presentation is often vague — fatigue, nausea, low mood, headache — and easily attributed to the cancer or to other treatment.
Adrenal insufficiency is the dangerous one: missed, it can present as collapse during an intercurrent illness.
- Check TSH and free T4 at baseline and regularly during checkpoint inhibitor treatment.
- In unexplained fatigue, hypotension or hyponatraemia, check a morning cortisol.
- Headache with fatigue suggests hypophysitis; assess pituitary hormones and consider imaging.
- Patients started on steroid replacement need sick-day rules and a steroid card.
Why it matters
Endocrine immune toxicities are often permanent but easily treated, and missing adrenal insufficiency can be fatal.
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