What is the most likely cause of worsening xerostomia and urinary retention in an older adult taking amitriptyline (Elavil, a tricyclic antidepressant) and an antiepileptic drug (AED)?

Differential Diagnosis

• Single most likely diagnosis
  • C. These are the known side effects of amitriptyline.
    • Justification: Amitriptyline is a tricyclic antidepressant (TCA) known for its anticholinergic side effects, which include dry mouth (xerostomia) and urinary retention. The patient's symptoms are consistent with these known side effects, making this the most likely explanation.
• Other Likely diagnoses
  • B. The patient has developed benign prostate hypertrophy.
    • Justification: Benign prostate hypertrophy (BPH) is a common condition in older adults that can cause urinary retention. While it's possible that the patient has developed BPH, the presence of dry mouth as a symptom makes amitriptyline side effects more likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • A. The patient stopped taking amitriptyline abruptly.
    • Justification: Although stopping amitriptyline abruptly is unlikely to cause dry mouth and urinary retention, it's essential to consider this possibility due to the risk of withdrawal symptoms, including seizures, which could be life-threatening in a patient with a history of seizures.
  • E. The dose of anticonvulsant was changed by his neurologist.
    • Justification: Changes in anticonvulsant medication or dosage can have significant effects on the patient's condition, including interactions with other medications like amitriptyline. While less likely to cause the specific symptoms mentioned, it's crucial to investigate any recent changes in medication to ensure the patient's safety.
• Rare diagnoses
  • D. His anticonvulsant medications are no longer working.
    • Justification: This option is less likely to be directly related to the symptoms of dry mouth and urinary retention. However, it's essential to consider the patient's overall condition, including their seizure history, to ensure that their anticonvulsant medications are effective. If the medications are no longer working, it could lead to an increase in seizures, which is a significant concern but not directly related to the symptoms presented.