Differential Diagnosis

• Single most likely diagnosis
  • Subacute combined degeneration (SCD) of the spinal cord: This condition is characterized by the loss of vibration sense and fine touch, which are typically carried by the dorsal columns of the spinal cord. The patient's symptoms, including numbness in the lower limbs, slippage of slippers while walking, loss of vibration sense below the umbilicus, and loss of fine touch below the knee, are consistent with SCD. The fact that temperature sense is intact and deep tendon reflexes (DTR) are intact also supports this diagnosis, as SCD typically spares these functions.
• Other Likely diagnoses
  • Peripheral neuropathy: This condition can cause numbness, tingling, and loss of sensation in the lower limbs. However, the specific pattern of sensory loss (loss of vibration sense and fine touch with intact temperature sense) is more suggestive of a central cause like SCD.
  • Spinal cord injury or compression: This could explain the patient's symptoms, especially if there was an injury or compression at a level that would affect the dorsal columns. However, the absence of any reported trauma or structural abnormalities on the CT scan makes this less likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Spinal epidural abscess or hematoma: These conditions can cause rapid progression of neurological deficits and can be life-threatening if not promptly treated. Although the patient's symptoms have been gradual, it is essential to consider these diagnoses due to their potential severity.
  • Cauda equina syndrome: This is a serious condition that requires urgent attention. It typically presents with a combination of low back pain, sciatica, and neurological deficits in the lower limbs, including sensory loss, weakness, and bladder/bowel dysfunction. The patient's symptoms do not fully align with cauda equina syndrome, but it should be considered due to its potential for severe and permanent neurological damage.
• Rare diagnoses
  • Vitamin B12 deficiency: This can cause subacute combined degeneration of the spinal cord, similar to the patient's presentation. However, it would be unusual for a patient with a history of lung cancer post-chemotherapy and radiation therapy to develop B12 deficiency without other systemic symptoms.
  • Tabes dorsalis: This is a rare condition characterized by degeneration of the dorsal columns of the spinal cord, typically due to untreated syphilis. It presents with loss of vibration sense, fine touch, and proprioception, but the patient's history does not suggest syphilis, making this diagnosis less likely.