Differential Diagnosis

• Single most likely diagnosis:
  • Intermittent lumbar radiculopathy: This is considered the most likely diagnosis due to the patient's presentation of chronic atraumatic bilateral posterior hip/buttock/proximal thigh pain, which is consistent with referred pain from the lumbar spine. The plan to obtain an MRI of the lumbar spine to evaluate for disc herniation or nerve impingement further supports this consideration.
• Other Likely diagnoses:
  • Sacroiliac (SI) joint dysfunction: The patient's symptoms and the discussion about considering an SI joint injection for both diagnostic and therapeutic purposes suggest that SI joint dysfunction is a plausible cause of his pain.
  • Underlying inflammatory process: Despite normal initial tests (ANA, rheumatoid factor, uric acid), the episode of unexplained left knee swelling and effusion raises the possibility of an inflammatory condition that may not have been fully evaluated or may be in a quiescent phase.
  • Labral tear: Although the labral tear found on the MRI of the left hip is noted, it is not considered a significant source of pain at this time. However, it remains a potential contributor to his symptoms.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Spinal infection or abscess: Although less likely, conditions such as a spinal epidural abscess or osteomyelitis could present with similar symptoms and would require urgent intervention.
  • Malignancy: The possibility of a malignancy affecting the spine, hip, or surrounding tissues, although rare, must be considered due to the potential severity of such conditions.
  • Neurological conditions (e.g., multiple sclerosis, cauda equina syndrome): These conditions could present with radicular symptoms and would have significant implications for management and prognosis.
• Rare diagnoses:
  • Spondyloarthritis: Conditions like ankylosing spondylitis could present with chronic back pain and intermittent joint effusions, although the patient's normal inflammatory markers make this less likely.
  • Osteonecrosis: Although the patient's age and lack of risk factors (e.g., steroid use, excessive alcohol consumption) make this less likely, osteonecrosis of the femoral head could cause hip pain and should be considered, especially if other diagnoses are ruled out.