The Authors Reply We thank you for the opportunity to provide a response to the concerns that were raised by Nagamine. As Nagamine mentioned, it is difficult to definitively distinguish between these two diseases using only blood tests.
Duloxetine use might indeed carry a risk of inducing falls in elderly people. Thus, in the present case, syncope and orthostatic hypotension in the five days preceding the incident might have occurred. However, at admission, we confirmed that there had been no obvious traumatic episode, such as a fall, and no intracranial lesions were revealed on head computed tomography (CT). In addition, no physical findings, such as dryness in the oral cavity or axilla, were evident on a physical examination, nor was any dehydration on blood tests found.
In most of the previous duloxetine-induced syndrome of inappropriate secretion of antidiuretic hormone (SIADH) cases, serum sodium levels improved with drug discontinuation and fluid infusion, as in this case. Duloxetine was discontinued, and extracellular fluid was infused on day 1 of hospitalization in this case, but hyponatremia worsened on day 2 of hospitalization, suggesting that SIADH had been aggravated by the infusion, as you mentioned. Therefore, we believe that SIADH was the main pathology in the present case.
As you mentioned, opportunities to prescribe duloxetine have been increasing. We also agree that electrolytes should be regularly measured, and information about traumatic episodes in elderly people, regardless of the presence of typical symptoms, should be regularly collected.
Thank you for your valuable comments. I am confident that they will be useful in our clinical practice in the future.
The authors state that they have no Conflict of Interest (COI).