Mechanisms of Edema Formation in Myxedema — Increased Protein Extravasation and Relatively Slow Lymphatic Drainage

TLDR

Inadequate lymphatic drainage may explain the exudates in serous cavities characteristic of myxedema. The study aimed to assess extravascular accumulation of albumin and fluid in primary myxedema by measuring metabolic turnover and transcapillary escape of 131I‑labeled human albumin in seven patients. This was achieved by measuring metabolic turnover and transcapillary escape of 131I‑labeled albumin in the patient cohort. In hypothyroid patients, plasma volume and albumin synthesis/catabolism were reduced, while transcapillary escape rate, extravascular albumin mass, and mean transit time were increased; all abnormalities normalized with l‑thyroxine, underscoring the role of extravascular albumin accumulation in myxedema edema.

Abstract

We assessed extravascular accumulation of albumin and fluid in primary myxedema by measuring metabolic turnover and transcapillary escape of 131I-labeled human albumin in seven patients. In the hypothyroid state, we found a low plasma volume (P less than 0.05), a reduced rate of albumin synthesis and catabolism (P less than 0.01), an increased transcapillary escape rate of albumin (P less than 0.01), a remarkable increase in the extravascular mass of albumin (1500 micronmol; P less than 0.01) and a longer mean transit time through the extravascular spaces in primary myxedema than in other states of generalized edema (P less than 0.05). All variables returned to normal during l-thyroxine treatment. The extravascular accumulation of albumin, and presumably of all other plasma proteins, is important in the generalized edema typically found in myxedema. Inadequate lymphatic drainage may also explain the formation of exudates in the serous cavities that are well known in myxedema.