Differential Diagnosis for 74-year-old with Abdominal Pain and Constipation

Single Most Likely Diagnosis

• Constipation due to Amitriptyline: Amitriptyline is a tricyclic antidepressant known to cause constipation as a side effect. Given the patient's recent use of this medication for headaches, it is plausible that the constipation is a direct result of the medication, potentially exacerbating or contributing to the abdominal pain.

Other Likely Diagnoses

• Diverticulitis flare-up: The patient has a history of diverticulitis, and abdominal pain could indicate a flare-up of this condition. Constipation can also be a symptom or contributing factor to diverticulitis.
• Medication-induced gastrointestinal side effects: Besides constipation, other gastrointestinal side effects from medications, including Amitriptyline, could contribute to abdominal pain.

Do Not Miss Diagnoses

• Bowel obstruction: Although less common, bowel obstruction is a serious condition that could present with abdominal pain and constipation. It's crucial to rule out this diagnosis due to its potential for severe complications.
• Colorectal cancer: Given the patient's age and symptoms of abdominal pain and constipation, colorectal cancer must be considered, even though it might not be the most likely diagnosis initially.
• Ischemic bowel disease: This condition can present with abdominal pain and changes in bowel habits. Given the patient's age, it's a critical diagnosis not to miss due to its high morbidity and mortality.

Rare Diagnoses

• Neurogenic bowel due to underlying neurological condition: Although Amitriptyline is prescribed for headaches, an underlying neurological condition could potentially cause neurogenic bowel, leading to constipation and abdominal pain.
• Gastrointestinal motility disorders: Conditions like gastroparesis or intestinal pseudo-obstruction could cause constipation and abdominal pain but are less common and would require specific diagnostic testing to confirm.