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A 23-year-old male was seen in the emergency department after suffering a concussion and head trauma from a motor vehicle accident. The patient was stabilized in the emergency department and transferred to the intensive care unit (ICU) for observation. The patient had computed tomography(CT) scan of the head that revealed a small amount of cerebral edema but was otherwise normal.

During the second day in the ICU, the nurse informed that the patient had a large amount of urine output in the last 24 hours. The nursing records reported his urine output over the previous 24 hours to be 5000 cc. He had not been given any diuretic medications. A urine osmolality was ordered and was found to be low. His physician remarked that the kidneys were not concentrating urine normally.

What is the most likely diagnosis for the increasing dilute urine output?

Which biochemical mediator is responsible for this disorder ?

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One Response to Case study- for self evaluation

  • Not very sure… But I'll give it a shot.

    The only disease I know so far that can cause dilute urine is Diabetes Insipidus. This is due to a decreased level of ADH (anti-diuretic hormone) in urine. ADH is anti-diuretic; therefore it prevents water loss in urine. When the hormone is deficient, excess diuresis occurs and excess water is lost in urine, resulting in dilute urine.
    [The biochemical basis is that ADH causes incorporation of water channels called Aquaporins from the cytoplasm to the plasma membranes of the nephron. This allows water reabsorption in tubules which otherwise are impermeable to water]
    ADH is secreted by the posterior lobe of the pituitary gland. The gland might have been damaged during the head injury. This leads to low levels of ADH and eventually, Diabetes Inspidus.

    The only point not supporting my diagnosis is the “otherwise” normal CT Scan. Head CT should have shown injury to the pituitary gland or to the hypophyseal stalk…