Our report presents multiple challenges with respect to identifying the unique imaging features that clinicians should be aware of while managing patients with simultaneous hyperparathyroidism and thyroid nodules, especially patients with kidney transplantation. PT-HPT can be observed in some patients with successful kidney transplantation. PT-HPT occurs in 45 and 20% of kidney transplantation recipients after 2 years and 5 years, respectively [
1]. The main cause of PT-HPT is enlarged and autonomous adenomas with dysregulated metabolic bone mineral parameters, even when the renal function of the allograft recovers to normal [
3]. Studies have reported that PT-HPT is associated with an elevated risk of fractures, cardiovascular disease, allograft loss (5%) and mortality (4%) [
4,
5,
11,
12]. Treatment for PT-HPT should be individualized, and parathyroidectomy should be considered.
Four orthotopic parathyroid glands are usually located behind the thyroid and originate from the third and fourth pharyngeal pouch. For successful parathyroidectomy, an accurate preoperative localization of the culprit parathyroid tissues is critical. Ectopic parathyroid adenomas occur in approximately 20 and 66% of patients with primary hyperparathyroidism and patients who undergo reoperation, respectively [
6]. IPA is rarely observed in certain locations in the parathyroid. The incidence of IPA has been reported to be 1.3–6.7% [
13,
14], but the literature has reported that the incidence of parathyroid adenomas located completely within the thyroid is less than 1%, and the most common location is inferior to the thyroid [
15]. Some scientists speculate that the primordium of the parathyroid gland was trapped and migrated within the thyroid, thus forming as an intrathyroidal parathyroid gland. Ultrasonography and
99mTcO
4-sestamibi SPEC/CT are the most common imaging modalities used to locate abnormal parathyroid glands. Ultrasonography can facilitate an excellent assessment of parathyroid adenomas (sensitivity: 76%, positive predictive value: 93%), but ultrasonography cannot detect ectopic sites, such as mediastinal, retroclavicular and retrooesophageal sites [
16]. Ultrasonography is also relatively insensitive in detecting concurrent thyroid nodules and has challenges in identifying IPA [
17]. Thyroid nodules occur in the endemic areas of up to 68% of all patients [
18]. In total, 3% of patients have occult papillary carcinoma, and the incidence increases with age [
19]. The incidence of thyroid papillary carcinoma in kidney transplant recipients is low, some studies evaluated that the incidence of thyroid cancer was 0.22–2.3% [
20,
21]. Although the hyperechoic line on the ventral surface of the nodule is an important clue for diagnosing IPA, our patient had no characteristic imaging features [
22]. Therefore, further evaluation was required with
99mTcO
4-sestamibi SPEC/CT, which has high sensitivity (84%) and positive predictive value (95%) and improves upon the detection rate of ultrasonography for ectopic lesions [
9]. In our case, ultrasonography only found one cystic parathyroid nodule without tracer uptake, and the left thyroid nodule was confirmed as papillary carcinoma by FNAB. Focal uptake in the right superior thyroid nodule on SPECT/CT is consistent with IPA due to persistent hyperparathyroidism after kidney transplantation. Some studies report that the combination of ultrasonography and
99mTcO
4-sestamibi SPECT can accurately locate IPA [
8‐
10,
23‐
27].
When IPA and multifocal papillary thyroid carcinoma are diagnosed in patients with kidney transplantation, no consensus guidelines exist for the best practices. Therefore, the decisions depend on the individual patient characteristics and the surgeons’ preferences, and the treatment would maintain normal calcium levels and renal function.
To the best of our knowledge, this is the first report of simultaneous IPA and multifocal papillary thyroid carcinoma in a patient with kidney transplantation. Although the precise localization and differential diagnosis of these conditions are challenging, the combination of ultrasonography, SPECT/CT and careful interpretation could help clinicians confirm the presence of IPA and papillary thyroid carcinoma.