Nyctohemeral variation and suppressibility of plasma ACTH in various stages of Cushing's disease.

In order to define nyctohemeral plasma ACTH secretory patterns, frequency plasma ACTH samples were obtained in seven patients with untreated Cushing's disease (i.e. pituitary-dependent Cushing's syndrome), five Cushing's patients treated by bilateral adrenalectomy, four of whom had Nelson's syndrome, and one patient with 21-hydroxylase deficiency (congenital adrenal hyperplasia). A nyctohemeral rhythm of plasma ACTH concentration was apparent in the one patient with the adrenogenital syndrome but not in those with Nelson's syndrome or Cushing's disease. The effect of graded doses of dexamethasone, 2,8 or 32 mg per 24 h period, on plasma ACTH concentrations was studied in patients with untreated or treated Cushing's disease or Nelson's syndrome. In all of these hypercorticotrophic states, the mean plasma ACTH concentraton was not significantly affected by the smallest dose of dexamethasone, was partially suppressed by the intermediate dose, and further suppressed by the largest dose. In contrst, the patient with congenital adrenal hyperplasia and elevated plasma ACTH concentrations showed complete suppression of plasma ACTH levels following the smallest dose of dexamethasone. These findings indicate that there is resistance to ACTH suppression by dexamethasone in all stages of Cushing's disease and suggest that negative feedback of glucocorticoids may be involved in the pathogenesis of this disease.

Apparently normal pituitary-adrenal suppressibility in Cushing's syndrome: dexamethasone metabolism and plasma levels.

In this study, we evaluated the responses of the pituitary-adrenal axis to the suppressive action of dexamethasone by relating plasma dexamethasone (Dex) and cortisol (F) levels in normal subjects and patients with Cushing's syndrome. Various doses of Dex were ingested at midnight as a single dose or at 6-hour intervals for 2 days beginning at 8 A.M. A nomogram was prepared by plotting the 8 A.M. plasma F concentration as a function of the plasma Dex value. Two patients with Cushing's syndrome had normal responses to Dex suppression as assessed by conventional tests. With the nomogram, we found that all patients with Cushing's syndrome, including these two, exhibited abnormally high plasma F values at some time during our evaluation. A decreased metabolic clearance rate of Dex appears to explain why one showed normal suppression. Another patient with bilateral adrenal hyperplasia showed sequentially over 13 months abnormal, normal, and abnormal suppression, which could not be attributed to an abnormality of Dex metabolism. We conclude that relating plasma Dex and F provides the investigator with a reliable index for evaluating resistance of the pituitary-adrenal axis to the suppressive effect of Dex.

Thoracic outlet syndrome with tetany of the hands.

A patient presenting with tetany was found to have thoracic outlet obstruction. This was treated by transaxillary first rib resection, and good relief of the carpal spasm was obtained. The mechanism whereby neurovascular compression may produce tetany is discussed.