Differential Diagnosis for Excessive Urination in a 6-Month-Old Boy
Single Most Likely Diagnosis
- B) Defect in ADH (vasopressin) receptor: The patient's symptoms of excessive urination (polyuria) and thirst (polydipsia), along with laboratory findings of hypernatremia (elevated sodium levels), low urine specific gravity (1.002), and elevated serum osmolality, are consistent with diabetes insipidus (DI). A defect in the ADH receptor, also known as nephrogenic diabetes insipidus, would lead to an inability to concentrate urine, resulting in the observed symptoms.
Other Likely Diagnoses
- A) Abnormal tubular sodium transport: While this could potentially lead to some of the observed electrolyte imbalances, it is less directly linked to the specific symptoms of polyuria and polydipsia in the context of the provided laboratory values.
- E) Renal tubular acidosis: This condition could explain some of the electrolyte disturbances but does not directly account for the polyuria and polydipsia without additional symptoms such as metabolic acidosis, which is not prominently featured in the case.
Do Not Miss Diagnoses
- Diabetic Ketoacidosis (DKA): Although the glucose level is elevated, it is not sufficiently high to immediately suggest DKA, and the absence of ketosis or significant acidosis in the provided information makes this less likely. However, DKA can present with polyuria and polydipsia, and missing this diagnosis could be fatal.
- Hyperaldosteronism: This condition, characterized by excessive aldosterone secretion, can lead to hypertension and hypokalemia. While the provided potassium level is low, the clinical context (e.g., absence of hypertension) and the specific symptoms do not strongly suggest this as a primary diagnosis.
Rare Diagnoses
- Psychogenic Polydipsia: Although rare in infants, this condition involves excessive water drinking leading to polyuria. It is less likely given the age of the patient and the specific laboratory findings.
- Other Rare Genetic Disorders: There are several rare genetic disorders that can affect renal function and lead to symptoms similar to those described. These would be considered if more common causes are ruled out and the patient's condition does not improve with standard treatments.