Kidney disease and thyroid dysfunction: the chicken or egg problem

Patients with non-dialysis-dependant chronic kidney disease (NDD-CKD) and dialysis-dependant chronic kidney disease (DD-CKD) frequently also suffer from thyroid disorders, especially hypothyroidism which is found two to five times more often among them compared to the general population. Emerging research has illustrated the potential prognostic implications of this association as NDD-CKD and DD-CKD patients with hypothyroidism have been shown to have higher mortality rates, and treatment of subclinical hypothyroidism in NDD-CKD patients has been reported to attenuate the decline of glomerular filtration rate over time. This review illustrates the bidirectional, multi-layered interplay between the kidneys and the thyroid gland explaining how pathologies in one organ will affect the other and vice versa. Additionally, it outlines the impact of thyroid disorders on routine parameters of kidney function (especially serum creatinine and serum cystatin C) that nephrologists should be aware of in their clinical practice. Lastly, it summarizes the emerging evidence from clinical studies on how treatment of subclinical hypothyroidism in NDD-CKD and DD-CKD patients may potentially have beneficial effects on kidney function as well as mortality. While most of the research in this area has been performed on adult patients, we specifically discuss what is currently known about thyroid dysfunctions in paediatric CKD patients as well and provide management suggestions. The evidence accumulated so far clearly indicates that further, prospective studies with meticulous methodology are warranted to refine our understanding of thyroid disorders in paediatric and adult CKD patients and establish optimal treatment pathways.