Updated: 1/31/2018

Syndrome of Inappropriate ADH (SIADH)

Topic
Review Topic
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Questions
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Evidence
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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
    • serum osmolality < 275 mOsm/kg
    • random urine sodium > 40 mEq/L
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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Questions (3)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
Calculator

(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? Review Topic

QID: 106822
FIGURES:
1

History of increased consumption of fluids

12%

(2/16)

2

Increased urine glucose

0%

(0/16)

3

Kidney unresponsive to antidiuretic hormone

6%

(1/16)

4

Increased antidiuretic hormone

75%

(12/16)

5

Decreased antidiuretic hormone

6%

(1/16)

M1

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PREFERRED RESPONSE 4
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(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?
Review Topic

QID: 100380
1

Aspirin overdose

13%

(11/84)

2

Diarrhea

5%

(4/84)

3

Diabetes insipidus

40%

(34/84)

4

Primary polydipsia

14%

(12/84)

5

Lung cancer

20%

(17/84)

M1

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PREFERRED RESPONSE 5
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