Polyuria and Polydipsia (Case 38)
Case: The patient is a 68-year-old woman with a medical history of hypertension, hyperlipidemia, and obesity. She presents to the outpatient office because for the last few weeks she has been more tired than usual and feels that she has been drinking more water. She has also been going to the bathroom more frequently, particularly at night. In addition, she has blurry vision and headaches. Her husband is also your patient. He has trouble maintaining control over his blood sugar and is also obese. Both the patient and her husband often miss scheduled follow-up appointments.
The patient’s medications are hydrochlorothiazide, atorvastatin, and an aspirin. Her father had hypertension and coronary artery disease, and her mother was recently diagnosed with type 2 diabetes mellitus. The patient works as an administrative assistant. She smokes half a pack of cigarettes a day and drinks a glass of wine occasionally.
On examination she is pleasant and conversant and appears comfortable. She states that she thinks she may have “a little sugar” like her husband. Her vital signs are within normal limits, but her body mass index (BMI) is 37. Her lungs are clear to auscultation, and heart sounds are normal. Her abdomen is obese. Her neurologic exam is normal except for a decreased monofilament sensation in her feet.
Diabetes mellitus, type 1
Diabetes mellitus, type 2
Diabetes insipidus (DI)
Polyuria is most often caused when the kidneys are subjected to an increased osmotic load, such as that from glucose or calcium. Alternatively, it may be due to endocrine disorders of fluid regulation such as vasopressin (antidiuretic hormone, ADH) deficiency. Conditions that cause bladder irritability or obstruction such as cystitis or prostatic enlargement can cause increased urinary frequency, but usually not polyuria. When most clinicians are assessing an obese patient with polyuria and polydipsia, type 2 diabetes mellitus, which affects over 20 million persons in the United States, is the first diagnosis that comes to mind. A point-of-care capillary glucose by finger-stick or a urinalysis can quickly make the diagnosis of uncontrolled diabetes, so that this patient can quickly get the appropriate care.
• Diabetes mellitus is diagnosed with two fasting blood glucose measurements greater than 125 mg/dL or a random value greater than 200 mg/dL in a patient with symptoms. At this point, you have to determine how sick the patient is and whether the patient needs inpatient management to treat symptomatic hyperglycemia or has life-threatening complications such as diabetic ketoacidosis (DKA) or a nonketotic hyperosmolar state.
• Patients with type 1 diabetes may present to the emergency department in DKA, with an elevated blood glucose, or an anion gap metabolic acidosis with positive serum ketones and electrolyte imbalances.
• In an asymptomatic patient, hyperglycemia may be an incidental finding on laboratory work done for other reasons, or it could be seen in a patient admitted to the hospital in acute stress (e.g., from a myocardial infarction or severe infection). At times, medications such as corticosteroids can be the cause.
• If a patient’s blood glucose has been consistently high for some time, symptoms such as polydipsia, polyuria, and nocturia can be seen, since excess glucose delivered to the kidneys causes an osmotic diuresis. Hyperglycemia can also manifest as blurry vision from the effects of glucose on the lens, or tingling and numbness in the toes from peripheral neuropathy. Other symptoms that should be sought are weight loss and fatigue.
• A patient who presents in DKA or a hyperosmolar state may be too sick to give a history but may have an obvious inciting insult such as infection or a myocardial infarction. Nausea, vomiting, and abdominal pain are common symptoms in patients with DKA.
• Patients with DI may have pituitary tumors; they should be questioned about headaches and visual changes, and other endocrinopathies. Patients with primary polydipsia may be drinking excessive amounts of water because of a psychiatric or central nervous system (CNS) disorder.
• Screening for chronic complications of diabetes should include a monofilament exam looking for sensory neuropathy, a foot exam assessing for peripheral vascular disease, and a dilated funduscopic exam screening for retinopathy.
• In a patient admitted to the hospital with DKA, Kussmaul respirations and ketotic breath may be noted; very sick patients may present with mental status changes and signs of volume depletion such as hypotension and tachycardia.