Not to worry PET, it’s not cancer.

Tanday R, Falinska A, Vakilgilani T, Ling Y, Todd JF


We present 2 patients who have increased uptake in the thyroid on PET imaging.

Mrs AN is a 76 year old woman with hypertension, atrial fibrillation, deep vein thrombosis and primary autoimmune hypothyroidism with positive TPO antibodies on thyroxine. When abroad she had a carotid USS which discovered a thyroid nodule.  Referred to us she was euthyroid with an USS finding of a 5mm calcified nodule with no vascularity in the right thyroid.  She had a FNA in Sept 12 and Jan 13 both revealing a lymphocytic infiltrate (Thy 2) consistent with Hashimoto’s thyroiditis.  She was reassured and discharged.  She was re-referred this autumn after a private FDG PET scan was performed to investigate night sweats and palpitations. This showed high focal uptake in the thyroid and nil else.  A repeat USS thyroid showed no change. 


Mr NM is a 45 year old man with a succinate dehydrogenase mutation and paragangliomas in the aorta (resected Sept 11), bilateral neck (left excised Nov 12) and primary autoimmune hypothyroidism with positive TPO antibodies on thyroxine.  FDG PET imaging consistently shows increased uptake in the left thyroid as well as the expected neuroendocrine tumours.  An ultrasound of the thyroid showed a bulky left lobe with a 8mm nodule. FNA cytology confirmed lymphocytic infiltrate (Thy2) consistent with Hashimoto’s thyroiditis.  MRI neck showed no significant lesion within the thyroid. 


Both our patients had increased uptake on FDG PET in the thyroid where there was no other clinical disease.  Both these patients had treated primary autoimmune hypothyroidism with the thyroid FNA cytologies confirming a lymphocytic thyroiditis.  It is important to be aware that increased uptake in the thyroid on PET maybe due to Hashimoto’s thyroiditis rather than a sinister cause.