The development of hyponatremia during LT4 withdrawal and low-iodine diet in otherwise healthy patients with thyroid carcinoma is extremely rare. However, elderly patients with metastatic thyroid carcinoma need observation during LT4 withdrawal combined with a low-iodine diet and should receive instruction to take iodine-free sodium chloride. Free water restriction may be necessary in some patients.

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Ventricular tachycardia in patients with phenochromocytoma is rare. We report a patient with a norepinephrine-secreting extra-adrenal pheochromocytoma who had exercise induced ventricular tachycardia. Prior to diagnosis, the patient was treated with a selective beta 1 blocker, atenolol, which resulted in suppression of the dysrhythmia and amelioration of the hypertension. This is the first reported case of selective beta blockade suppressing ventricular tachycardia in a patient with a pheochromocytoma. Electrocardiographic abnormalities described in patients with pheochromocytoma are reviewed.

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Although the action of gastric inhibitory polypeptide (GIP) on the beta cells of the pancreas is well documented, the effect of this hormone on insulin secretion in patients who are hypothyroid has not been studied. Hypothyroid patients demonstrate increased serum immunoreactive insulin levels in response to oral glucose when compared with euthyroid subjects. We postulated that a delayed and exaggerated response of GIP could account for the hyperinsulinaemic response. Nine thyroidectomized patients (aged 44.9 +/- 3.6 years) who were otherwise healthy but undergoing re-evaluation for recurrence of thyroid carcinoma, were given a 75 g oral glucose tolerance test (OGTT). These subjects were studied 6 weeks after thyroid hormone replacement had been stopped and while on hormone treatment. The serum glucose and plasma GIP responses to oral glucose were similar in the euthyroid and hypothyroid states. The serum insulin response as well as the areas under the curve for insulin following OGTT were significantly elevated (P < 0.01) during hypothyroidism. Solid-phase gastric emptying times studied in six patients who were euthyroid and hypothyroid were not different (35 +/- 12 versus 36 +/- 14 min respectively). None of the subjects had detectable levels of serum thyroglobulin, microsomal or parietal cell antibodies. In summary, we have confirmed a hyperinsulinaemic response to an OGTT and normal solid-phase gastric emptying rates in this form of hypothyroidism. We did not find significant differences in serum glucose or GIP responses and postulate this as evidence of resistance to the effects of endogenous insulin. The mechanism of alterations in carbohydrate tolerance in the hypothyroid state continue to remain unknown.

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Myxedema coma is a rare condition associated with high mortality. The pathophysiology is complex and often involves profound hypothyroidism as well as an inciting event. The diagnosis should be suspected based on the clinical presentation, and treatment should not be delayed while awaiting confirmatory laboratory data. In critically ill patients, laboratory differentiation between severe hypothyroidism and the euthyroid-sick syndromes is difficult and may require measurement of free hormone levels. Treatment consists of correction of electrolyte abnormalities, passive rewarming, treatment of infections, respiratory and hemodynamic support, administration of stress-dose glucocorticoids, and thyroid hormone replacement. Intravenous thyroxine, between 200 and 500 micrograms as the initial dose followed by 50 to 100 micrograms/day, is recommended. Concurrent therapy with triiodothyronine can also be considered.