Evaluation of thyroid dysfunction in patients with nephrotic syndrome
Background. Thyroid and kidney are interdependent on each other in many ways for optimal functioning of either organs. Proteinuria causes urinary loss of thyroid hormones and thyroid binding globulins in substantial amount resulting in subclinical/overt hypothyroidism. Autoimmunity, which can attack both the organs simultaneously, may also contribute considerably to the abnormal functioning of both organs.
Aims and objectives. To study the effect of proteinuria on the thyroid function and its association with autoimmunity.
Methods. The study was carried out on a total number of 60 patients with nephrotic range proteinuria attending the kidney and dialysis clinic PGIMS, Rohtak, India. Thyroid profile and baseline investigations along with Anti-TPO antibodies and renal biopsy were carried out on each patient. Patients were allocated to 2 groups based on Anti TPO antibody results: group A comprising 25 Anti-TPO Ab positive patients and group B comprising 35 Anti-TPO Ab negative patients.
Results. Group A patients with Anti TPO antibody positivity had more elevated TSH levels (p<0.0001), proteinuria (p=0.0011) and serum creatinine (p=0.0137) as compared to group B patients. Group A patients had more diminished eGFR (p=0.0127) and serum albumin (p=0.0056) than patients in group B. TSH levels were positively correlated with proteinuria r=0.55 (p<0.0001, 95% CI 0.35 to 0.70) and serum creatinine levels r=0.56 (p<0.0001, 95% CI 0.36 to 0.71). TSH levels were negatively correlated with serum albumin levels r=-0.52 (p<0.0001, CI -0.68 to -0.31) and glomerular filtration rate r=-0.54 (p<0.0001, CI -0.69 to -0.33). On histopathology, membranous nephropathy - 29 out of 60 patients, 48% - was the most common finding in both the groups.
Conclusions. Nephrotic range proteinuria leading to thyroid dysfunction is a common entity but the association with autoimmunity causes an exaggerated effect on both these organs. Our study established a significant correlation between thyroid autoimmunity and nephrotic syndrome. Thus, a high index of suspicion should be kept in all patients with nephrotic syndrome to look for any associated antibodies against thyroid antigens. Autoimmunity causes more proteinuria and more elevations of thyrotropin leading to clinical hypothyroidism; however, the occurrence of overt hypothyroidism necessitating treatment needs further study.