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

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<0.05), a reduced rate of albumin synthesis and catabolism (P<0.01), an increased transcapillary escape rate of albumin (P<0.01), a remarkable increase in the extravascular mass of albumin (1500 μmol; P<0.01) and a longer mean transit time through the extravascular spaces in primary myxedema than in other states of generalized edema (P<0.05). All variables returned to normal during /-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. (N Engl J Med 301:460–465, 1979)