Thyrotropin concentration in hypopituitarism

Abstract

Johnston and colleagues (Jan 4, p 26)1Johnston S Hoult S Cham CA Falling again.Lancet. 1997; 349: 26Summary Full Text Full Text PDF PubMed Scopus (5) Google Scholar report an elderly man with hypopituitarism. The final sentence reads “the possibility of hypopituitarism should be considered in any elderly person presenting with the combination of hypotension, hyponatraemia, and a low serum thyroxine with an unsuppressed thyrotropin concentration”. This statement is obviously incorrect. A low thyroxine would not be expected to suppress thyrotropin. Instead, hypopituitarism (ie, secondary hypothyroidism) should be suspected whenever a low serum thyroxine is coupled to an unincreased thyrotropin value—ie, a level that can be either low or inappropriately normal despite a low thyroxine concentration. In fact, the finding on the first admission of a borderline low concentration of thyroxine coupled to an inappropriately normal thyrotropin might have suggested the request of a thyrotropin-releasing hormone stimulation test, to verify the possibility of secondary hypothyroidism. Johnston and colleagues (Jan 4, p 26)1Johnston S Hoult S Cham CA Falling again.Lancet. 1997; 349: 26Summary Full Text Full Text PDF PubMed Scopus (5) Google Scholar report an elderly man with hypopituitarism. The final sentence reads “the possibility of hypopituitarism should be considered in any elderly person presenting with the combination of hypotension, hyponatraemia, and a low serum thyroxine with an unsuppressed thyrotropin concentration”. This statement is obviously incorrect. A low thyroxine would not be expected to suppress thyrotropin. Instead, hypopituitarism (ie, secondary hypothyroidism) should be suspected whenever a low serum thyroxine is coupled to an unincreased thyrotropin value—ie, a level that can be either low or inappropriately normal despite a low thyroxine concentration. In fact, the finding on the first admission of a borderline low concentration of thyroxine coupled to an inappropriately normal thyrotropin might have suggested the request of a thyrotropin-releasing hormone stimulation test, to verify the possibility of secondary hypothyroidism. Thyrotropin concentration in hypopituitarismAuthor's reply Full-Text PDF