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Syndrome of Inappropriate ADH (SIADH)

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Topic updated on 03/20/17 10:56am

Snapshot
  • SCLCA 48-year-old female presents to the emergency room with mental status changes. Laboratory analysis of the patient's serum shows: Na+ 122 mEq/L, K+ 3.9 mEq/L, HCO3- 24 mEq/L, BUN 21 mg/dL, Creatinine 0.9 mg/dL, Ca2+ 8.5 mg/dL, Glucose 105 mg/dL. Urinalysis shows: Osmolality 334 mOsm/kg, Na+ 45 mEq/L, Glucose 0 mg/dL. Sputum cytology is shown.
Introduction
  • SIADH is a syndrome characterized by an
    • increased ADH production
    • an increased sensitivity to ADH
  • Pathogenesis
    • causes
      • paraneoplastic syndromes
        • small cell carcinoma of the lung  
          • cancer cells produce ADH ectopically
      • CNS disturbances
        • infection, stoke, tumor, trauma, hydrocephalus
      • may also be cause by drugs
        • NSAIDS, antidepressants, chemotherapy, clofibrate, narcotics, carbamazepine
Presentation
  • Symptoms
    • mental status changes 
      • caused by cerebral edema
Evaluation
  • Labs 
    • hyponatremia
      • secondary to dilutional effects of increase water resorption
      • ADH increases aquaporin insertion in the collecting duct of the renal tubule
    • urine osmolality > 100 mOsm/kg
      • urine is always concentrated despite decreasing serum osmolarity
    • random urine sodium > 40
Treatment
  • Moderat symptoms - Lifestyle
    • fluid restriction (not salt restriction)
  • Moderate - severe symptoms - Pharmacologic
    • demeclocycline
      • induces ADH insensitivity
        • specifically works at the vasopression type-2 receptor (V2R) 
      • can be used in patients with small cell carcinoma
      • not routinely used
    • conivaptan, tolvaptan
      • ADH antagonist
    • consider hypertonic saline (use cautiously)
    • normal saline + diuretic (furosemide)
Complications
  • Central pontine myelinolysis (CPM)
    • result of too rapid correction of hyponatremia


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Qbank (2 Questions)

TAG
(M1.EC.75) A 57-year-old female presents to the emergency department with complaints of nausea, muscle aches, and confusion that presented and worsened over the past several days. On further probing, she also reports a nagging cough with shortness of breath and a 10-lb. weight loss over the last 3 months. She does not have a primary care doctor and denies having regular check ups. She reports smoking 1 pack of cigarettes per day and denies any alcohol consumption. Her medical history is significant for hypertension, a 30 pack year smoking history, and anxiety. Vital signs are as follows: T 37.2 C, HR 86, BP 137/86, RR 14, and SpO2 96%. Physical examination shows normal skin turgor, moist mucus membranes, and no peripheral edema. A CT scan is performed to investigate the patient's cough in Figure A. Lab work is performed in the ED and the findings are below.
Na: 128 mEq/L
Plasma osmolality: 260 mOsm/kg
Urine osmolality: 250 mOsm/kg
Urine Na: 47 mEq/L

Which of the following is most likely also found in this patient? Topic Review Topic
FIGURES: A          

1. History of increased consumption of fluids
2. Increased urine glucose
3. Kidney unresponsive to antidiuretic hormone
4. Increased antidiuretic hormone
5. Decreased antidiuretic hormone

PREFERRED RESPONSE ▶
TAG
(M1.EC.79) A 48-year-old female presents to the emergency room with mental status changes.
Laboratory analysis of the patient's serum shows:
Na 122 mEq/L
K 3.9 mEq/L
HCO3 24 mEq/L
BUN 21 mg/dL
Cr 0.9 mg/dL
Ca 8.5 mg/dL
Glu 105 mg/dL

Urinalysis shows:
Osmolality 334 mOsm/kg
Na 45 mEq/L
Glu 0 mg/dL

Which of the following is the most likely diagnosis?
Topic Review Topic

1. Aspirin overdose
2. Diarrhea
3. Diabetes insipidus
4. Primary polydipsia
5. Lung cancer

PREFERRED RESPONSE ▶
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SIADH by Osmosis
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