Differential Diagnosis for a 39-year-old Veteran with Lower Back Pain and Neurological Symptoms

Single Most Likely Diagnosis

• Herniated Nucleus Pulposus (HNP) with Cauda Equina Syndrome: The patient's symptoms of a sudden "pop" in the lower back followed by progressive worsening, right leg numbness, and difficulty urinating are highly suggestive of a herniated disc compressing the spinal nerves, potentially leading to cauda equina syndrome. This condition is a medical emergency due to the risk of permanent neurological damage.

Other Likely Diagnoses

• Lumbar Disc Protrusion without Cauda Equina Syndrome: Similar to the most likely diagnosis but without the severe neurological deficits associated with cauda equina syndrome. The patient's symptoms could still be due to a disc protrusion causing nerve root compression.
• Lumbar Strain or Sprain: The initial "pop" could be indicative of a muscle or ligament injury in the lower back, which might not fully explain the neurological symptoms but could be a contributing factor.
• Degenerative Disc Disease: Pre-existing degeneration of the spinal discs could predispose the patient to herniation or could be causing the symptoms directly, especially if there's significant nerve root compression.

Do Not Miss Diagnoses

• Spinal Epidural Abscess: Although less likely, this is a potentially deadly condition that requires immediate attention. Symptoms can include back pain, neurological deficits, and systemic signs of infection.
• Spinal Tumor: Either primary or metastatic tumors could cause similar symptoms by compressing the spinal cord or nerve roots.
• Infectious Discitis or Osteomyelitis: Infection of the disc or vertebral body could present with back pain and neurological symptoms, especially if the infection compresses or destroys adjacent neural structures.

Rare Diagnoses

• Arachnoiditis: Inflammation of the arachnoid membrane surrounding the spinal cord could cause pain, numbness, and difficulty with bladder control, although it's less common and often associated with a history of spinal surgery, infection, or trauma.
• Spinal Hematoma: A collection of blood within the spinal canal could compress the spinal cord or nerve roots, leading to neurological symptoms. This is rare but could be seen in the context of trauma or anticoagulation.