Thyroiditis (subacute De Quervain, postpartum, on immunotherapy)

Laboratory tests

• TSH
• Free T4
• CRP
• TSH receptor antibodies (if doubt with Graves' disease)if neededAtypical presentation (mild pain, normal CRP): TRAb are positive in Graves' disease, absent or low in subacute thyroiditis ^[2,3].

Later, after the painful phase

• TSH

Laboratory tests

• TSH
• Free T4
• TSH receptor antibodies (if TSH low: exclude Graves' disease)if neededPostpartum thyrotoxicosis: TRAb distinguish Graves' disease from thyroiditis, especially during breastfeeding, when scintigraphy is not possible ^[1].
• Anti-TPO antibodies (if TSH raised, in the absence of a previous positive result)if neededHypothyroid phase: positive anti-TPO antibodies indicate an autoimmune cause ^[1]; a previous positive result is not rechecked ^[8].

Before the first injection, then before each course (first 3 to 6 months)

• TSH
• Free T4 (anti-CTLA-4, or unexplained low TSH)if neededRisk of hypophysitis with central hypothyroidism, especially on anti-CTLA-4: low TSH with low free T4 ^[10].
• 8 am serum cortisol (if low TSH with low free T4, before any levothyroxine)if needednon-French guidelineLow TSH with low free T4 on immunotherapy: think of hypophysitis. The ESE (2022) and the UK Society for Endocrinology (2018) ask for cortisol deficiency to be excluded before any levothyroxine, which can trigger an adrenal crisis ^[11,12]. The 2018 French opinion on the thyroid does not address this point ^[10]; see the page "Treatment: cancer immunotherapy".
• Anti-TPO antibodies (if TSH between 5 and 10 mIU/L)if neededHypothyroidism with TSH < 10 mIU/L: anti-TPO antibodies help to decide on levothyroxine ^[10].
• TSH receptor antibodies (severe thyrotoxicosis or diagnostic doubt)if neededWhen in doubt between drug-induced thyroiditis and another cause of hyperthyroidism, in particular if the thyrotoxicosis is severe ^[10].
• Then: TSH every 2 months for 6 months, then if symptoms.