Serum N-terminal Pro-B-Type Natriuretic Peptide and Phosphodiesterase 4D Levels in Adults With Overt Hypothyroidism:...

Thyroid hormone regulates cardiac and vascular function, and overt hypothyroidism predisposes to impaired ventricular relaxation, raised systemic vascular resistance, and heart failure with preserved ejection fraction. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a sensitive marker of myocardial wall stress and is itself under thyroid-hormone control, while cyclic-nucleotide phosphodiesterases (PDEs) shape the intracellular signalling that underlies myocardial contractility. The two have rarely been measured together in adults with overt hypothyroidism and seldom in India. We compared serum NT-proBNP and phosphodiesterase 4D (PDE4D), a cAMP-specific isoform, between adults with overt hypothyroidism and euthyroid controls.

This hospital-based case-control study at a tertiary-care teaching hospital in north India was conducted with institutional ethics committee approval and written informed consent. We enrolled 80 adults (older than 20 years) in equal, age- and sex-matched overt hypothyroid and euthyroid groups (40 each). Blinded personnel measured serum triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), and NT-proBNP by chemiluminescent immunoassay and serum PDE4D by a sandwich enzyme-linked immunosorbent assay. Groups were compared with the independent-samples t-test or Mann-Whitney U test and the chi-square or Fisher's exact test, alongside univariable logistic regression and effect-size analysis (point-biserial r, Cramer's V); p < 0.05 was taken as significant.

The groups matched closely for age (p = 0.617) and sex (72.5% female in each). Serum NT-proBNP ran about fourfold higher in the hypothyroid group (927.10 ± 487.47 vs 233.32 ± 126.12 pg/mL; p < 0.001; r = 0.70), while serum PDE4D ran about twofold lower (19.0 ± 5.9 vs 38.7 ± 9.7 ng/mL; p < 0.001; r = 0.78); PDE4D gave the highest Nagelkerke R² of any variable studied (0.884). The two markers thus moved in opposite directions. The hypothyroid group also carried higher BMI and blood pressure and more hypertension (35% vs 10%) and peripheral oedema (45% vs 20%).

In adults with long-standing overt hypothyroidism, serum NT-proBNP was markedly higher and serum PDE4D markedly lower than in euthyroid controls, a reciprocal pattern set against raised blood pressure, BMI, and hypertension. Cardiovascular surveillance in overt hypothyroidism may therefore be worthwhile, and serum PDE4D emerges as a promising, hypothesis-generating candidate marker that still needs prospective, multivariable-adjusted validation.