Differential Diagnosis for Complete Loss of Sensation at the Left Knee and Below
Single Most Likely Diagnosis
- Lumbar Syrinx or Tarlov Cyst: A condition where a fluid-filled cavity forms within the spinal cord, potentially causing sensory loss without motor deficits due to the selective involvement of sensory tracts.
Other Likely Diagnoses
- Lumbar Disc Herniation: Specifically, a herniation at the L2-L3 or L3-L4 level could compress sensory roots, leading to sensory loss below the knee without motor weakness if the motor roots are spared.
- Diabetic Radiculopathy or Neuropathy: Diabetes can cause selective damage to sensory nerves, leading to loss of sensation. However, this typically presents with other symptoms such as pain or would be part of a broader neuropathic pattern.
- Vitamin B12 Deficiency: Can cause subacute combined degeneration of the spinal cord, leading to sensory loss, but usually, there are other symptoms such as weakness, gait difficulties, or upper motor neuron signs.
Do Not Miss Diagnoses
- Spinal Cord Infarction or Ischemia: Although less common, spinal cord infarction can present with sudden onset of sensory loss without motor deficits if the anterior spinal artery is spared. This is a medical emergency.
- Spinal Dural Arteriovenous Fistula (SDAVF): A condition where there's an abnormal connection between arteries and veins in the spinal cord, leading to venous congestion and potentially selective sensory loss. It's crucial to diagnose and treat to prevent progression.
- Multiple Sclerosis (MS): While MS can present with a wide range of neurological symptoms, a relapse could potentially cause selective sensory loss. Given its potential for significant disability, it's essential not to miss this diagnosis.
Rare Diagnoses
- Sjögren's Syndrome with Neuropathy: An autoimmune disorder that can cause neuropathy, including sensory neuropathy, though it's less common and usually accompanied by other systemic symptoms.
- Tabes Dorsalis (Neurosyphilis): A late manifestation of syphilis that affects the spinal cord, causing loss of sensation, particularly proprioception and pain. It's rare due to the availability of effective treatments for syphilis.
- Copper Deficiency Myelopathy: Similar to vitamin B12 deficiency, copper deficiency can cause a myelopathy with sensory ataxia and loss of vibration and position sense, but it's exceedingly rare.