Beiglböck H, Wolf P, Pfleger L, et al. - Provided that energy-rich phosphorus-containing metabolites (PM) and phospholipids (PL) may be affected by thyroid hormone action and may be non-invasively measured by 31P nuclear magnetic resonance spectroscopy, researchers conducted the longitudinal, prospective pilot study for measuring the actions of peripheral thyroid hormones on PM and PL tissue concentrations. Nine patients with hyperthyroidism and four patients with hypothyroidism were examined at baseline and three months post-treatment. Thyroxine has a clear negative correlation with PDE concentrations in liver and skeletal muscle. A reduction in PDE in hypothyroidism and an increase in hyperthyroidism have resulted in the normalization of thyroid dysfunction. Therefore, to estimate tissue-specific peripheral thyroid hormone action, PDE may be a sensitive tool.