Endocrine Abstracts

Case history: A 53-year-old woman presented with vasculitic rash affecting her limbs. She has a 3-year history of thyrotoxicosis. Having developed intolerance to carbimazole she was maintained on propylthiouracil (PTU) for the last two years. Imaging results were consistent with multinodular goitre. Thyroid stimulating immunoglobulin was negative. A few months prior to this presentation she developed dysphagia. Repeat imaging showed an 8 cm right thyroid nodule that grew significantly from multiple coalescing nodules detected 3 years previously. Tracheoesophageal deviation with right vocal cord paresis was apparent. Cytology following fine needle aspiration was consistent with Thy3a.

Investigations: Admission blood tests showed microcytic anaemia – Hb 98 g/l (normal range (NR) 115–160), MCV 79fl (NR 80–100) and neutropenia 0.89 × 10⁹/; (NR 2–8). Thyroid function tests showed TSH <0.02 mU/l (NR 0.27–4.2), free T4 (fT4) 19.0 pmol/l (NR 12–22) and free T3 (fT3) 6.8 pmol/l (NR 3.1–6.8). Vasculitic screen showed atypical anti-neutrophil cytoplasmic antibodies (ANCA), PR3 28 iu/ml (NR 0–1.9), MPO 7.2 iu/ml (NR 0–3.4). Lupus anticoagulant, ANA, ENA, dsDNA and complement levels were normal.

Results and treatment: Prednisolone was commenced with minimal improvement. After PTU was withdrawn, the vasculitic rash improved and neutropenia resolved. Seven days after PTU cessation there was clinical and biochemical evidence of worsening thyrotoxicity; fT4 increased to 66.4 pmol/l. Due to limited medical treatment options available total thyroidectomy was planned to allow symptom control and histopathological evaluation of the thyroid gland. Lugol’s iodine and beta blockade were commenced to optimise thyroid function pre-operatively. FT4 subsequently decreased to 47.2 pmol/l, 26.9 pmol/l and 22.3 pmol/l on days 2, 7 and 10 of treatment respectively. Total thyroidectomy was performed on day 11 with no complications. Macroscopically the right thyroid lobe was twice the size of the left. Diffuse hyperplasia of thyroid follicles, cystic changes with calcifications were present microscopically without features of thyroiditis or malignancy. TSH and fT4 were <0.02 mU/l and 17.4 pmol/l respectively on Levothyroxine replacement one-week post-op.

Conclusions and point for discussion: PTU-induced ANCA vasculitis (AAV) is an uncommonly encountered complication. Endocrinologists need to be vigilant as it can occur independent of PTU dose or length of exposure. Timely recognition is crucial as prompt PTU discontinuation is key. The conundrum faced in this case reflects the complexity when planning alternative treatment post PTU cessation. The presence of Thy3a nodule made total thyroidectomy a necessity, however the timeframe for surgery was influenced by patient-related factors including variable degrees of thyrotoxicity and AAV treatment such as steroids or immunosuppressive therapy.