Challenging Diagnosis of Postpartum Thyroiditis and Co-Existing Thyroid Nodule

ABSTRACT Objective: Postpartum thyroiditis presents as thyrotoxicosis from autoimmune thyroid inflammation that causes release of iodothyronines and diffuse, decreased thyroid uptake of both radioactive iodine and 99mTc-pertechnetate. Thyroiditis with focal “cold” thyroid nodule on thyroid scintigraphy has been previously described and attributed to localized inflammation. Methods: We report a patient diagnosed with postpartum thyroiditis, in whom an apparently “hot” nodule on initial thyroid pinhole scintigraphy was later noted to be “cold” at follow-up imaging. Results: Thyroid nodularity co-existing with subacute thyroiditis usually presents as focal “cold” nodules, attributed to localized inflammation in the thyroid. The diagnosis of postpartum thyroiditis in our patient was made more challenging due to the presence of a thyroid nodule with an evolving imaging appearance over time. This led to a potential for misdiagnosis of this “hot” nodule dependent on the timing of having the thyroscintigram performed early in the disease course. We hypothesized that the overactive focus of uptake was due to sparing of a pre-existing colloid nodule by the inflammatory process which later became “cold” in the recovery phase. Conclusion: The presence of co-existing thyroiditis and thyroid nodules, both common entities, may cause diagnostic difficulty on thyroid scintigraphy due to dynamic, temporal changes in imaging appearance and the variable findings reported in the literature. Clinical surveillance and performing repeat thyroid imaging will allow correct diagnosis and appropriate management of these challenging cases. Abbreviation: RAIU radioactive iodine uptake