What is the most likely diagnosis for a 61-year-old male with a history of mild constipation, presenting with severe abdominal cramps, inability to pass stool for 4 days, and radiographic findings of air-fluid levels and distal fecal impaction, who responded well to treatment with Miralax (polyethylene glycol) and Senna, along with magnesium citrate?

Differential Diagnosis

• Single most likely diagnosis
  • Fecal impaction: The patient's history of mild constipation, recent onset of severe constipation, and inability to pass stool, along with the CT scan findings of a large amount of stool in the distal colon, support this diagnosis. The patient's response to laxatives and normal bowel movements after treatment also suggest fecal impaction.
• Other Likely diagnoses
  • Constipation-induced ileus: The patient's symptoms and CT scan findings could also be consistent with an ileus caused by constipation. The patient's history of opioid use, which can cause constipation, and the recent onset of severe constipation, support this diagnosis.
  • Dehydration-induced constipation: The patient admitted to not hydrating well in the days leading up to the onset of constipation, which could have contributed to the development of constipation.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Intestinal obstruction: Although the CT scan suggested that an underlying stricture or mass would not be excluded, the patient's response to laxatives and normal bowel movements after treatment make this diagnosis less likely. However, it is still important to consider and rule out intestinal obstruction due to its potential severity.
  • Colorectal cancer: Although the patient has no family history of colorectal cancer or polyps, it is still important to consider this diagnosis, especially given the patient's age and symptoms.
  • Volvulus: The patient's symptoms and CT scan findings could also be consistent with a volvulus, although this is less likely given the patient's response to laxatives.
• Rare diagnoses
  • Sigmoid stricture: The CT scan suggested an area of narrowing in the sigmoid colon, which could be due to a stricture. However, this is less likely given the patient's response to laxatives and normal bowel movements after treatment.
  • Neurogenic bowel: The patient's mother has Parkinson's disease, which could suggest a possible genetic component to neurogenic bowel. However, this is less likely given the patient's symptoms and response to treatment.