Differential Diagnosis
- Single most likely diagnosis
- Lithium carbonate: The patient's symptoms of intense thirst, polydipsia (drinking 6 to 8 L of water daily), and polyuria (significantly increased urine output) are classic signs of nephrogenic diabetes insipidus, a known side effect of lithium therapy. Lithium can affect the kidneys' ability to concentrate urine, leading to these symptoms.
- Other Likely diagnoses
- Diabetes insipidus (central or nephrogenic, not related to medication): Although the patient's serum hemoglobin A1c is well-controlled, the presence of polyuria and polydipsia could suggest diabetes insipidus. However, the normal basic metabolic panel and the absence of other symptoms make this less likely.
- Psychogenic polydipsia: The patient's history of bipolar disorder could contribute to psychogenic polydipsia, where excessive water intake is driven by psychological factors rather than a physiological need. However, the significant increase in urine output and low urine osmolality suggest a physiological rather than psychological cause.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Hypercalcemia: Although the basic metabolic panel is within normal limits, hypercalcemia can cause nephrogenic diabetes insipidus and should be ruled out, especially in patients taking lithium, as it can increase calcium levels.
- Kidney disease or renal failure: The patient's symptoms could be indicative of underlying kidney disease or renal failure, which would require prompt attention and treatment.
- Rare diagnoses
- Sjögren's syndrome: This autoimmune disorder can cause nephrogenic diabetes insipidus, but it is rare and would typically be accompanied by other symptoms such as dry mouth and eyes.
- Other medications: Although less likely, other medications such as demeclocycline or amphotericin B can cause nephrogenic diabetes insipidus, but these are not part of the patient's current regimen.