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Hyponatremia in a patient with type 1 diabetes
Many conditions can cause low sodium levels.
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A 52-year-old woman with type 1 diabetes came to see me for a follow-up visit.
The patient had broken her humerus a few months ago and she had been briefly hospitalized two days prior to seeing me to have the fixation screws operatively removed. Moreover, she had traveled to rural China for a month prior to seeing me.
Apart from widely fluctuating blood glucose levels during her recent hospitalization, the patient described some fatigue and mild pain after the humerus operation but felt well otherwise. She specifically denied weight loss, diarrhea or lightheadedness.
Other medical conditions included dyslipidemia, diabetic nephropathy with microalbuminuria and history of seizure in the setting of hypoglycemia.
The patient was using an insulin pump with aspart. She confirmed that her usual medications had not changed and included simvastatin, ramipril and a multivitamin in addition to the insulin. She denied use of alcohol, nicotine or recreational drugs. The patient was single and worked as a school counselor. She stated that she exercised 45 minutes twice a week, but she had not done so for the past six weeks due to travel and the hospitalization.
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Her physical exam was rather unremarkable, except for a tender right upper arm. Blood pressure was 116 mm Hg/74 mm Hg, heart rate 49, respiratory rate 14, weight 150 lb (stable from last visit, normal BMI). Mucus membranes were moist, there was no leg edema, and the patient did not appear to exhibit orthostatic symptoms when changing position.
Routine labs revealed an HbA1c of 6.5%, normal Chem12 except for a low Na of 128 meq/L (normal: 135-145), creatinine 0.7 mg/dL. She had a LDL of 62 and triglycerides were 71. Fingerstick glucose in the office was 176 mg/dL three hours after her last meal.
The patient’s Na had been 140 to 142 over the past three years. The patient was asked to have a repeat blood draw to recheck her sodium level, and a low Na of 129 was confirmed one day later.
What would you do for this patient?
- Order a blood alcohol level to exclude beer potomania.
- Ask the patient in greater detail about her travel history and whether she is taking any analgesic medications.
- Forbid all exercise, because sweating may worsen the hyponatremia.
- Start fish oil capsules, 1 g four times a day.
- Hospitalization to evaluate the patient for polydipsia.
CASE DISCUSSION
This is a case of mildly symptomatic hyponatremia discovered on routine chemistry, if one wants to ascribe the fatigue to that condition.
The first response should always be to confirm the lab value. The next step is to think about the volume status of the patient. In this case, she appeared to be euvolemic.
A call to the patient (answer B) revealed that she had been taking naproxen for her postoperative pain. In addition, I inquired whether she had been drinking distilled water during her trip to China (she replied that she had been drinking bottled water). Naproxen, like other NSAIDs, has been associated with hyponatremia. Since her pain had been getting better, she agreed to hold the medication. Serum osmolality and urine electrolytes may also help in the evaluation of the hyponatremic patient, but were not drawn in this case.
Follow-up Na six days later revealed a Na of 140 meq/L, and the patient has been doing well since. Extreme pain or other stress can also cause hyponatremia by way of syndrome of inappropriate antidiuretic hormone secretion.
Strenuous exercise can indeed lead to severe hyponatremia, especially if the athlete is not repleting sufficient sodium during exercise (option C). This effect has been described in marathon runners. While our patient did exercise, she did so in moderation and had not exercised at all in the weeks prior to her visit.
Polydipsia (usually due to psychiatric disease) with a hypotonic beverage may also lead to hyponatremia (option E), but this was not one of the patient’s complaints during the visit. In a similar vein, consumption of large quantities of beer, a hyponatremic beverage, has also been associated with hyponatremia.
This is rather unlikely in a patient who does not really drink any alcohol (option A). Hypertriglyceridemia may cause pseudohyponatremia, but the patient’s triglyceride levels are normal, and her blood glucose levels (hyperglycemia can also be associated with hyponatremia) are at goal. Fish oil capsules are therefore not warranted at this point (option D).
Ronald Tamler, MD, PhD, MBA, is an Assistant Professor in the Division of Endocrinology at Mount Sinai School of Medicine, N.Y.