What is the Differential Diagnosis of Hypokalemia?
A 14-year-old male came to the emergency room after he had an episode of loss of consciousness for 1-2 minutes.
He regained consciousness on the way to the emergency room.
He said he felt his heart racing and then loss consciousness. He has had 1 previous episode 9-12 months ago where he felt “shaky and weak”. Over the past month he has complained of general “weakness” but cannot describe it further. he says he has had fatigue for 4-5 years.
He has missed some school because of the weakness. He has also had some muscle cramps that were short-lived.
The family history was positive for heart attacks at an advanced age and some anxiety and depression. No arrhythmias or neurological problems were in the family.
The review of systems was negative including fever, recent illnesses, travel, unusual diets or eating behaviors, and sexual activity.
The pertinent physical exam reveals a well-developed adolescent with normal vital signs and growth parameters. He has normal skin and subcutaneous fat. HEENT had a normal dental examination. His heart had a normal rate and rhythm with no murmurs and good pulses.
He had a normal neurological evaluation. His mood revealed some minor symptoms of depression. The rest of his examination was normal.
The laboratory evaluation in the emergency room showed a potassium level of 2.6 mEq/L (normal 3.4-4.7 mEq/L) and magnesium of 1.0 mEq/L (normal 1.3-2.0 mEq/L).
He received potassium and magnesium supplementation by IV. An electrocardiogram was normal and his beta-HCG was negative. The rest of his laboratory evaluation was normal at that time including electrolytes, BUN, creatinine, phosphorous, glucose, liver and pancreatic enzymes.
He was hospitalized and repeated electrolytes, BUN, creatinine, glucose, creatinine phosphokinase, urinalysis, urine electrolytes and osmolality were negative.
An abdominal ultrasound and urine toxicology screen were also normal.
Consultation with cardiology and neurology were negative.
A screening evaluation for psychiatric illness confirmed some concerns for depression but a fuller evaluation was needed.
A nephrology consult was obtained and the diagnosis of Gitelman’s syndrome was considered.
As the patient’s clinical course had shown no abnormalities since initial presentation, he was discharged to home on oral potassium and magnesium.
He was to follow up with his local physician, psychiatrist and nephrologist for further evaluation and monitoring.
Gitelman syndrome is a renal salt-wasting disorder that causes volume contraction and hypokalemia alkalosis. Hypomagnesemia occurs in ~50% of patients. It is an autosomal recessive disorder. Patients are born full term without polyhydramnios have normal weight gain and usually present in late childhood. They often crave salt. They may present with tetany or weakness secondary to hypomagnesemia. They also have low urinary calcium excretion.
Treatment is potassium and magnesium supplementation.
Bartter syndrome is often confused with Gitelman syndrome. Bartter syndrome also is a renal salt-wasting disorder that is autosomal recessive. These patients often have a history of polyhydramnios and prematurity. They commonly have failure to thrive in the first year of life. Older children also crave salt and may complain of muscle cramps or constipation because of chronic volume depletion secondary to renal salt losses.
Treatment is centered on electrolyte supplementation but hypotonia and failiure to thrive can be difficult to treat.
Potassium is important for cellular homeostasis and is the most common intracellular cation. Most potassium is intracellular and total body potassium is ~50 meq/kg of body weight. The kidney is the final homeostatic mechanism for total body potassium.
Potassium is filtered in the kidney and ~80% is reabsortion in the proximal tubule. Potassium is secreted in the descending limb of Henle
with reabsorbing in the ascending limb. Potassium is again secreted in the distal tubules and collecting duct. Overall renal handing of potassium is affected by urine flow rate, plasma and luminal potassium concentration, delivery of sodium and chloride, availability of other nonabsorbable ions (e.g. sulfate, phosphate) and diuretics.
The differential diagnosis of hypokalemia includes:
- Gastrointestinal losses – normally the bowel secretes potassium into the lumen and reabsorbs sodium chloride
- Nasogastric suctioning
- Pyloric stenosis
- Enema and laxatives
- Enteric fistula
- Villous adenoma
- Biliary system
- Biliary drainage
- Renal losses
- Electrolyte abnormalities
- Endocrine abnormalities
- Cushing disease or syndrome
- Congenital adrenal hyperplasia
- High renin states
- Increased mineralocorticoid – medications such as Florinef®, chewing tobacco, licorice
- Intrinsic renal abnormalities
- Bartter’s Syndrome
- Gitelman’s Syndrome
- Renal tubular acidosis, types I or II
- Antibiotics – e.g. amphotericin B, carbenicillin
- Diuretics – especially thiazide, loop diuretics, osmotic diuretics
- Electrolyte abnormalities
- Shift to Intracellular space
- Barium intoxication
- Familial hypokalemia Periodic Paralysis
- Na-K-ATPase stimulation – e.g. beta-2 agonists, catecholamines, insulin
- Excessive sweating
- Inadequate intake – e.g. anorexia nervosa or abnormal diets, over long time periods only 10 meq/L/day of K is sufficient to sustain life
Questions for Further Discussion
1. What is the laboratory evaluation for hypokalemia?
2. What is the differential diagnosis for hyperkalemia?
Fluid and Electrolyte Balance
To Learn More
To view pediatric review articles on this topic from the past year check PubMed.
Information prescriptions for patients can be found at MEDLINEplus for this topic: Metabolic Disorders
To view current news articles on this topic check Google News.
Bakerman S. Bakerman’s ABC’s of Interpretive Laboratory Data. 3rd Edit. Interpretive Laboratory Data, Inc. Myrtle Beach, SC. 412.
Rudolph CD, et.al. Rudolph’s Pediatrics. 21st edit. McGraw-Hill, New York, NY. 2003:1652-53,1713.
ACGME Competencies Highlighted by Case
1. When interacting with patients and their families, the health care professional communicates effecively and demonstrates caring and respectful behaviors.
2. Essential and accurate information about the patients is gathised.
3. Informed decisions about diagnostic and thisapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
4. Patient management plans are developed and carried out.
8. Health care services aimed at preventing health problems or maintaining health are provided.
9. Patient-focused care is provided by working with health care professionals, including those from othis disciplines.
10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.
23. Differing types of medical practice and delivery systems including methods of controlling health care costs and allocating resources are known.
24. Cost-effective health care and resource allocation that does not compromise quality of care is practiced.
25. Quality patient care and assisting patients in dealing with system complexities is advocated.
26. Partnering with health care managers and health care providers to assess, coordinate, and improve health care and how these activities can affect system performance are known.
Donna M. D’Alessandro, MD
Associate Professor of Pediatrics, Children’s Hospital of Iowa
February 6, 2006