Thyroid hormone changes in chronic spinal cord injury.

Spinal cord injury (SCI) impacts metabolic function and deranges various hormonal axes. Previous studies characterizing thyroid hormones in SCI reported depressed triiodothyronine (T3) and thyroxin (T4), primarily in acute tetraplegics. These studies cited an 11-13 percent incidence of low T3 syndrome (LT3S) in SCI patients, with an increased incidence in tetraplegics (20-36 percent). The purpose of this study was to evaluate thyroid function and determine the incidence and clinical relevance of LT3S in the chronic SCI population. Thyroid function tests were performed on 30 chronic SCI patients (14 tetraplegics and 16 paraplegics) and 30 age- and gender-matched controls. Mean T3 and T4 levels were significantly depressed in SCI patients relative to controls, while T3 resin uptake (T3RU) values were significantly elevated. LT3S only occurred in the SCI population with an incidence of 23.3 percent. SCI patients with LT3S did not differ significantly from those without in the level or completeness of injury, age or the interval since injury. They did, however, have co-existent pathology: decubiti, urinary tract infections, etc. When SCI patients with normal T3 were compared with controls, they still had depressed mean T3 levels. We conclude that LT3S occurs frequently in the chronic SCI population and suggest that depressed serum T3 levels may predispose SCI patients to sick euthyroidism in the face of minor pathologic insult.