Posterior Pituitary - ADH, Diabetes Insipidus MCQs

The three main causes are Alveolar rupture with dissection of air into the mediastinum; Perforation or rupture of the esophagus, trachea, or main bronchi; and Dissection of air from the neck or the abdomen into the mediastinum. There is severe substernal chest pain with or without radiation into the neck and arms. The physical examination usually reveals subcutaneous emphysema in the suprasternal notch and Hamman's sign, which is a crunching or clicking noise synchronous with the heartbeat and is best heard in the left lateral decubitus position. The diagnosis is confirmed with the chest radiograph. Usually no treatment is required, but the mediastinal air will be absorbed faster if the patient inspires high concentrations of oxygen. If mediastinal structures are compressed, the compression can be relieved with needle aspiration.

Oral thrush (due to Candida infection appears as a white, cheesy exudate, often on an erythematous mucosa in the posterior oropharynx. While most commonly seen on the soft palate, early lesions are often found along the gingival border Reference: Harrison's Principles of Internal Medicine 21 st Ed, Ch: 216, Pg: 1672

This patient has developed hypovolemia from fluid losses from vomiting and diarrhea. There is no evidence that other osmotically active compounds have been ingested, thus serum osmolality is likely to be low. Because of hypovolemia, ADH (and aldosterone) will be stimulated, and serum ADH levels will be high. The kidney will be resorbing water and Na, and urine Na concentration will be low. Intravenous volume repletion with normal saline is advisable. Reference: Harrisons Principles of Internal Medicine, 21 st Ed, Ch:53 Pg: 342

The diagnosis is likely to be diabetes insipidus . The causes for polyuria in a patient include primary polydipsia, central DI and Nephrogenic DI Diagnosis of DI in a patient with polyuria (urine output more than 50 ml/kg) is suggested by high plasma osmolality (>295 mOsm/kg) in a patient passing dilute urine ( urine osmolality If the diagnostic thresholds of DI are not met, DI can be confirmed by a water deprivation test where failure of urine concentration would be expected. During this test a patient is not allowed to drink and plasma ADH, plasma osmolality and urine osmolality are measured. A therapeutic trial of DDAVP is only appropriate if a diagnosis of DI is confirmed (On the water deprivation test) and helps to differentiate between cranial or nephrogenic diabetes insipidus. Reference : Harrison's Principles of Internal Medicine 21 st edition Page 2921

The patient has drug induced Diabetes Insipidus based upon increased urine output, low urine osmolality, high plasma osmolality. This is most likely to be caused by lithium. Drugs causing diabetes insipidus: Lithium Aminoglycosides Methoxyflurane Amphotericin B Demeclocycline Cisplatin Rifampin Foscarnet Drugs like carbamazepine and chlorpropamide has been linked with SIADH resulting in hyponatremia Reference : Harrison's Principles of Internal Medicine 21 st edition Page 2920

Fine-tuning of salt and water balance is achieved in the distal and collecting tubules under the influence of aldosterone and antidiuretic hormone (ADH). ADH, however, plays a central role in urinary concentration by increasing the water permeability of the normally impermeable cortical and medullary collecting tubules. In the absence of ADH, little water is reabsorbed in the collecting tubules and dilute urine is excreted. ADH mediated water reabsorption from the collecting tubules is facilitated via aquaporin 2 channels on the luminal surface. Around 15-20% of renal water reabsorption is ADH mediated. Reference : Harrison's Principles of Internal Medicine 21 st edition Page 2919

Hemorrhage in anterior & preoptic hypothalamus may cause acute hyperthermia accompanied by paradoxical vasoconstriction & tachycardia. Lesion in posterior hypothalamus could lead to hypothermia. Hypothalamic nuclei and their functions Anterior - thermoregulation Preoptic - thermoregulation, sexual behavior Supraoptic - vasopressin and oxytocin secretion Paraventricular - oxytocin and vasopressin production Suprachiasmatic - circadian rhythm regulation Ventromedial - satiety centre Posterior - thermoregulation and arousal Arcuate - secretion of releasing hormones of hypothalamus Lateral hypothalamus - hunger centre Reference : Harrison's Principles of Internal Medicine 21 st edition Page 2905

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a disorder of impaired water excretion caused by the inability to suppress the secretion of antidiuretic hormone (ADH). In SIADH, the urine sodium excretion is high. Hyponatremia (ie, serum Na +