Rosen & Barkin's 5-Minute Emergency Medicine Consult (203 page)

• Hypokalemia
  
• Hypothyroidism
  
• Myasthenia Gravis
  
• Systemic Lupus Erythematosus
  

CODES

• 710.3 Dermatomyositis
  
• 710.4 Polymyositis
  

BASICS

• Disorder in which large volumes of dilute urine are excreted (polyuria) as an inappropriate response to arginine vasopressin (AVP)
  
• Polyuria defined as >3 L in 24 hr
  
• Often characterized by excessive fluid intake (polydipsia)
  
• 2 types:
  
  • Central diabetes insipidus (DI, CDI; failure or deficiency of AVP release):
    
    • 4 types:
      
      • No AVP to release (loss or malfunction of posterior pituitary neurons)
        
      • Defective osmoreceptors—release AVP only in response to severe dehydration
        
      • Elevated threshold for AVP release
        
      • Subnormal amount of AVP released
        
    • Familial cases have been reported (autosomal dominant).
      
  • Nephrogenic DI (lack of renal response to AVP):
    
    • Differentiate from primary polydipsia.
      
    • Some cases are X-linked recessive in males.
      

• Central DI:
  
  • Any condition that disrupts the osmoreceptor-hypothalamus-hypophyseal axis:
    
  • Highest incident in ages 10–20 yr
    
    • Trauma (skull fractures, hemorrhage)
      
    • Pituitary or hypothalamic surgery
      
    • CNS neoplasm: DI can be considered a tumor marker:
      
      • Pituitary adenomas
        
      • Craniopharyngiomas
        
      • Germinomas
        
      • Pinealomas
        
      • Meningiomas
        
    • Metastatic tumors:
      
      • Leukemia/lymphoma
        
    • Granulomatous:
      
      • Histiocytosis
        
      • Sarcoidosis
        
    • Congenital CNS defects
      
    • CNS infections (e.g., meningitis, encephalitis)
      
    • Pregnancy (Sheehan syndrome)
      
    • Idiopathic (autoantibodies, occult tumor)
      
    • Wolfram syndrome (DI, DM, optic atrophy, deafness)
      
    • Ethanol
      
• Nephrogenic DI:
  
  • Any condition that disrupts the kidney:
    
    • Congenital renal disorders
      
    • Obstructive uropathy
      
    • Renal dysplasia
      
    • Polycystic kidney disease
      
    • Systemic disease with renal involvement
      
    • Sickle cell disease
      
    • Sarcoidosis
      
    • Amyloidosis
      
    • Drugs:
      
      • Amphotericin
        
      • Phenytoin
        
      • Lithium (most common and persists past discontinuation of drug)
        
      • Aminoglycosides
        
      • Methoxyflurance
        
      • Demeclocycline
        
    • Electrolyte disorders:
      
      • Hypercalcemia
        
      • Hypokalemia
        

• Transient in the 2nd trimester:
  
  • Unclear etiology, but there is an increase of circulating vasopressinase.
    
  • Leads to a decrease in AVP and transient DI
    
  • Watch patient closely during anesthesia and periods of water restriction.
    
  • Typically clears after 2–6 wk after delivery
    
  • Desmopressin (DDAVP) resists this vasopressinase.
    
• Sheehan syndrome may cause DI.
  

DIAGNOSIS

• Polyuria (up to 16–24 L/d of urine):
  
  • Note the voiding frequency.
    
• Polydipsia (often craves cold fluids):
  
  • Note the amount of PO fluid intake per day.
    
• Drug ingestion
  
• Signs and symptoms of hypothalamic tumors:
  
  • Headache
    
  • Visual disturbances
    
  • Growth disturbances
    
  • Obesity
    
  • Hyperpyrexia
    
  • Sleep disturbances
    
  • Sexual precocity
    
  • Emotional disturbances
    

• Dehydration
  
• Cachexia
  
• Head trauma
  
• Visual field defects
  
• Seizures
  

• Polyuria and polydipsia may not be recognized by caregivers until symptoms of dehydration develop.
  
• In neonates:
  
  • Often present at birth
    
  • If unrecognized, dehydration and hypernatremia may cause permanent CNS damage.
    
• In infants:
  
  • Irritability
    
  • Poor feeding/weight loss
    
  • Constipation
    
  • Growth failure
    
  • Intermittent high fever
    
  • Abnormal behavior (hyperactivity, restlessness, excessive crying)
    
• In children:
  
  • Enuresis
    
  • Difficulty with toilet training
    

• Clinical diagnosis in the ED:
  
  • Elevated serum sodium concentration
    
  • Copious amounts of dilute urine
    
• History:
  
  • Usually an increased amount of PO fluid intake per day
    
  • Voiding frequency
    
  • Medication use history
    
• Physical exam
  
• Labs below
  

• Urinalysis:
  
  • Specific gravity will be low.
    
• Serum and urine osmolality:
  
  • High serum osmolality
    
  • Low urine osmolality
    
• Electrolytes, BUN, creatinine, and glucose:
  
  • Hypernatremia
    
  • Hypercalcemia
    
  • Hypokalemia
    
• CBC:
  
  • Anemia may be a sign of a neoplasm.
    
• Serum and urine AVP tests are expensive and unnecessary in the ED.
  

• As needed to evaluate for trauma or search for neoplasm
  
• CXR
  
• CT of brain
  
• MRI of pituitary axis is usually outpatient.
  

Water deprivation test (dehydration test):

• Unnecessary in the emergency setting
  
• Can be dangerous in cases of hypotension or small children
  
• Performed as a confirmatory test for those receiving treatment
  
• Measures urine and plasma osmolality after fluid restriction
  
  • Urine osmo <300 is significant for DI
    
    • Desmopressin is administered
      
      • Central DI—urine osmo increased by >50%
        
      • Nephrogenic DI—urine osmo increased by <50%
        
  • Further testing is needed if urine osmo 300–800
    
  • Primary polydipsia if urine osmo >800
    

• Primary water deficit:
  
  • Inadequate access to free water
    
  • Increased insensible water loss (e.g., premature infants)
    
  • Inadequate breast-feeding
    
• Primary sodium excess:
  
  • Excessive sodium bicarbonate during resuscitation
    
  • Hypernatremic enemas
    
  • Ingestion of seawater
    
  • Hypertonic saline administration
    
  • Accidental substitution of salt (sodium chloride) for glucose in infant formulas
    
  • Intentional salt poisoning
    
  • High breast milk sodium
    
• Primary polydipsia (psychogenic polydipsia):
  
  • Solute-induced polyuria
    
  • Diuretic use
    
  • Resolving acute renal failure
    
  • Osmotic diuresis
    
  • Uncontrolled
    DM
    

TREATMENT

• ABCs
  
• Immobilize if trauma is suspected.
  
• Serum blood glucose
  
• IV access and fluids if signs of dehydration exist
  
• Control seizures according to medical direction guidelines.
  

• Manage ABCs.
  
• Manage traumatic injuries accordingly.
  
• High index of suspicion for head trauma
  

• Correction of hypotension:
  
  • Use of 0.9% NaCl is indicated for shock.
    
  • Intravascular losses represent only about 1/12 of total water losses.
    
• Central DI (vasopressin deficient):
  
  • AVP (aqueous vasopressin):
    
    • Half-life is too short.
      
    • May induce coronary vasospasm
      
    • Used only for dehydration test
      
  • Lysine vasopressin (lypressin):
    
    • Can be given intranasally
      
    • Frequent instillation needed
      
  • Desmopressin:
    
    • Drug of choice to control symptoms
      
    • Administer intranasally, SC, IV, or PO in 2 divided doses as necessary to control polyuria or polydipsia.
      
    • Caution in postoperative patients as cerebral edema may develop
      
  • Chlorpropamide (Diabinese):
    
    • Enhances effect of vasopressin at renal tubule
      
    • May stimulate AVP release
      
    • Useful only in partial CDI
      
    • Clofibrate stimulates the release of endogenous vasopressin.
      
• Nephrogenic DI:
  
  • Diuretics:
    
    • Induce natriuresis
      
    • Thiazides 1st line
      
    • Amiloride often used in combination with thiazides
      
  • Dietary sodium restriction
    
  • Restrict solutes and avoid excessive drinking to prevent water intoxication.
    
  • Avoid alcohol (especially beer) intake.
    
  • Check daily weights.
    
  • NSAIDs (indomethacin)
    
• Parenteral correction of initial water deficit in cases where PO is not an option:
  
  • Usually only in symptomatic hypernatremic cases
    
  • For fluid replacement, refer to “Hypernatremia.”