Differential Diagnosis for Acute Lower Back Pain

The patient's presentation of acute lower back pain following a fall, with a reported "snap" and exacerbation of pain with certain movements, suggests a musculoskeletal or spinal injury. The absence of leg pain radiation and urinary incontinence, but presence of significant constipation, guides the differential diagnosis.

• Single Most Likely Diagnosis
  • Muscle Strain or Lumbar Sprain: The mechanism of injury (twisting and lifting) and the nature of the pain (localized to the back and side, exacerbated by movement) are consistent with a muscle strain or lumbar sprain. The patient's age and the fact that he heard a "snap" could also suggest a possible ligamentous injury.
• Other Likely Diagnoses
  • Lumbar Disc Herniation: Although the patient denies radiation of pain to the legs, a disc herniation could still be possible, especially if the herniation is not significantly compressing a nerve root. The constipation could be related to pain or discomfort rather than a neurological deficit.
  • Vertebral Compression Fracture: Given the patient's age and the mechanism of injury, a vertebral compression fracture is a possibility, especially if the patient has osteoporosis or other risk factors for fracture.
• Do Not Miss Diagnoses
  • Cauda Equina Syndrome: Despite the patient's denial of urinary incontinence and leg pain, cauda equina syndrome (CES) must be considered due to the significant constipation, which could indicate a neurological deficit. CES is a medical emergency requiring prompt intervention.
  • Spinal Infection (e.g., Discitis or Osteomyelitis): The patient's report of chills and possible fever, in combination with back pain, raises concern for a spinal infection, which would require urgent medical attention.
  • Abdominal Aortic Aneurysm: Although less likely given the mechanism of injury, an abdominal aortic aneurysm could present with back pain and should be considered, especially in an older adult.
• Rare Diagnoses
  • Spinal Epidural Hematoma: A rare condition that could present with acute back pain and neurological deficits, although the patient's current symptoms do not strongly suggest this diagnosis.
  • Pathological Fracture: If the patient has an underlying malignancy or other bone disease, a pathological fracture could be a consideration, although this would be less likely without a known history of such conditions.

Imaging Recommendations

Given the acute onset of symptoms following a traumatic event and the patient's age, initial imaging should include:

• X-rays of the Lumbar Spine: To evaluate for fractures, dislocations, or other bony abnormalities.
• MRI of the Lumbar Spine: This is the most sensitive test for soft tissue injuries, including disc herniations, ligamentous injuries, and spinal cord or nerve root compression. It can also help identify infections or tumors.
• CT Scan of the Lumbar Spine: If an MRI is not available or contraindicated, a CT scan can provide detailed images of the bony structures and can help identify fractures or other bony abnormalities.

The choice of imaging should be guided by the clinical presentation and the suspected diagnosis, with consideration for the patient's overall condition and any potential contraindications to certain imaging modalities.