Primary hyperparathyroidism and non-medullary thyroid cancer- A review

Background: The association of thyroid disease and primary hyperparathyroidism is well described, with thyroid carcinoma being reported in 2-15% of cases. The most commonly associated carcinoma is non-medullary thyroid cancer. While the association of PHPT and medullary thyroid cancer (MCT) is well known, that of NMTC, despite its increasing incidence, is still not established. Our study is a review of incidence and underlying mechanisms of non-medullary thyroid cancer associated with PHPT. Also, best imaging tools for concomitant diagnosis is reviewed to ensure an adequate plan of care. Methods & findings: A search was done using two databases: Medline & Embase. The search conducted from the period of 2008 until April 2018 yielded a total of 142 studies. After an adequate screening, 26 studies were reviewed.  Incidence of DTC in association with PHPT in the literature ranged between 0.91% and 17.6%. The main histological thyroid malignancy found is micropapillary carcinoma. Despite its less aggressive presentation, these microcarcinomas may grow or develop nodal metastases on follow up. Although bilateral neck exploration with hemi/total thyroidectomy carries the risk of temporary recurrent laryngeal nerve injury or hypoparathyroidism, permanent complications are rare especially when compared to re-do neck surgery. Recently, parathyroid surgeries are going towards minimal invasive procedures, requiring an adequate imaging tool to ensure diagnosis of both diseases. Multiple risk factors for concomitant diseases were hypothesized, the more robust are the common embryologic origin and activation of angiogenic growth factors. Conclusion: NMTC is frequently associated with PHPT especially in endemic goiter areas. With the high prevalence of micropapillary carcinoma and its risks, a partial/total thyroidectomy in addition to parathyroidectomy may be warranted. With the recent need of adequate diagnostic tools, combining both Technetium Sestamibi scintigraphy and thyroid ultrasound improved sensitivities and accuracy of diagnosis, but dual-isotope scintigraphy (I-123 sodium iodide/ 99mTc-sestamibi) seems an attractive modality in hyperparathyroid patients with concomitant suspicious thyroid nodules. However, further studies for validation may be needed.