Endocrine Abstracts

A 56 year old lady was investigated by her GP for arthralgia and found to be thyrotoxic (TSH < 0.01 mU/l, free T4 34.8 (10–20 pmol/l), TPO 50 (<35 IU/ml)). She gave a history of anterior uveitis some 20 years earlier. She was commenced on carbimazole and referred to the endocrinology clinic, where her thyroid function rapidly normalised and a biochemical diagnosis of subacute thyroiditis was made. Thyroid pertechnatate scan showed reduced uptake throughout the gland. TSH receptor antibodies were negative. It was noted she had had a similar episode 11 years earlier. Investigations for breathlessness revealed some ground glass appearances on CT. Two further episodes of thyroiditis occurred, each one asymptomatic. She was found to be MPO-ANCA positive, for which prednisolone and subsequently mycophenolate mofetil was commenced for a diagnosis of microscopic polyangiitis. Eleven years later she developed hypothyroidism, presumed following another episode of thyroiditis, and levothyroxine commenced with normalisation of thyroid function, and a plan for radioiodine treatment if further episodes occurred. Microscopic polyangiitis is a small vessel necrotising vasculitis typically affecting the lungs, kidneys, eyes and other vascular beds, and most commonly associated with MPO-ANCA positivity. The understanding of the relationship between the thyroid and vasculitis is evolving. It is well recognised that ANCA positivity (MPO, PR3 or both) can occur frequently with thiouracil derivates more often than MMI derivatives, and that 15% of these patients can exhibit a clinical vasculitis, though presentation is heterogeneous. In addition, thyroid disease seems to occur more frequently in patients with vasculitis, perhaps up to 40% with ANCA positive vasculitis. Those of MPO positivity and female sex and are more likely, with the most common outcome being hypothyroidism. The link is not established, though theories include genetic predisposition, loss of tolerance to peroxidases and cross reactivity of TPO and MPO. Unfortunately studies lack details about the specifics of hyperthyroid episodes so the frequency of thyroiditis over other causes is not clear. There is also a lack of pathological data looking at the thyroid in patients with vasculitis. Recurrent thyroiditis is rare, with cases associated with amiodarone, suppurative thyroiditis and postpartum thyroiditis. To our knowledge this is the first case reported of recurrent thyroiditis associated with vasculitis.