SIADH

ü  ADHà 腎的V2à distal tubule and collecting ductàfree water retention and dilutional hyponatremiaà elevated urine osmolality in the setting of a low plasma osmolality

※ Essential diagnostic criteria:

ü  Plasma osmolality <275 mOsm/kg

ü  Urine osmolality >100 mOsm/kg and urine Na >20 to 40mEq/L

ü  Euvolemia

ü  Normal renal, adrenal, and thyroid function tests

ü  No recent use of diuretic agents

※ Euvolemic hypotonic hyponatremia:

ü  The most common cause of euvolemic hypotonic hyponatremia is SIADH.

ü  Characterized by low to normal total body sodium and normal to elevated total body water.

²  Hypothyroidismà dysregulation of ADH release or clearance, effects on vascular tone, cardiac output, and renal blood flow

²  Adrenal insufficiencyà caused by the loss of negative feedback on ADH secretion

²  Primary polydipsia

²  Potomania

²  Thiazide diuretics

²  Reset osmostat syndromeà shift in the set-point for ADH

²  Nephrogenic syndrome of inappropriate antidiuresisà mutations in the renal vasopressin V2 receptor causing increased water resorption，表現同SIADH但ADH測不到

ü  SIADH is usually self-limited, and the primary management strategy is to correct the underlying etiology.

ü  Loop diureticsà增加free water 排出、讓腎對ADH反應下降àenhance the effect of solute loading

ü  Demeclocycline acts on the renal collecting tubules to diminish responsiveness to ADH. The major side effect is nephrotoxicity.

ü  Vasopressin receptor antagonists exert their activity on renal V2 receptors resulting in a selective water diuresis without affecting sodium excretion

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Subclinical hyperthyroidism

原因：同甲亢

ü   Autoimmune thyroid disease

ü   Autonomous thyroid tissue

ü   TSH-mediated hyperthyroidism

ü   Human chorionic gonadotropin-mediated hyperthyroidism

ü   Thyroiditis

ü   Ectopic hyperthyroidism

會影響：

ü   The skeleton (bone resorption) and the cardiovascular system (increased risk of atrial fibrillation, heart failure, pulmonary hypertension, and angina) are the major target tissues adversely affected.

ü   Subclinical hyperthyroidism may also be associated with an increased risk of dementia.

評估：病史、用藥、PE

ü   Patients on suppressive levothyroxine therapyàTSH低是目標

ü   Patients on T4 for the treatment of hypothyroidismà不可以讓TSH太低

ü   女人要問有沒有懷孕，停經後或有骨鬆風險，可做骨密度檢查作為決定要不要治療的參考依據。

ü   沒吃T4的patients，persistently subnormal TSH values，如考慮藥治療，we obtain a radioactive iodine uptake and scan to help determine the etiology. 如有不只一處increased uptake, this could account for the low serum TSH. 如果沒有吸收，the etiology of subclinical hyperthyroidism may be thyroiditis or recent iodine exposure.

ü   Most patients with thyroiditis require no treatment.

ü   Patients at high risk for complications：(>65 years of age, with risk factors for cardiac arrhythmias, and postmenopausal women with or at risk for osteoporosis)
èIf TSH <0.1 mU/L, we treat the underlying cause of subclinical hyperthyroidism.
èIf TSH is 0.1 to 0.5 mU/L, we suggest treatment if there is underlying cardiovascular disease or if the bone density is low.

ü   Patients at low risk for complications：
èIf TSH <0.1 mU/L, we treat the underlying cause if the patient has symptoms suggestive of hyperthyroidism and/or if a thyroid radionuclide scan shows 不只一處吸收。
èf TSH is 0.1 to 0.5 mU/L, 觀察就好

ü   In observed patients, we measure TSH, free T4, and T3 every six months

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