Vitamin B12 Deficiency Causes Bilateral Spastic Paraparesis
The correct answer is C: Vitamin B12 deficiency. Vitamin B12 deficiency causes subacute combined degeneration affecting the corticospinal tracts bilaterally, resulting in spastic paraparesis with upper motor neuron signs including hyperreflexia, spasticity, and extensor plantar responses (Babinski sign) 1.
Why the Other Options Are Incorrect
Cerebellar Disease (Option A) - Incorrect
- Cerebellar lesions produce ataxia, dysmetria, and intention tremor—not spastic paraparesis 1
- The cerebellum does not contain upper motor neurons or corticospinal tracts, so it cannot produce the spasticity and hyperreflexia characteristic of bilateral spastic paraparesis 1
Peripheral Neuropathy (Option B) - Incorrect
- Peripheral neuropathies affect lower motor neurons and produce flaccid weakness with hyporeflexia or areflexia 1
- This is the opposite of spastic paraparesis, which requires upper motor neuron involvement with hyperreflexia and spasticity 1
Parkinson Disease (Option D) - Incorrect
- Parkinson disease is a basal ganglia disorder causing bradykinesia, rigidity, and tremor—not spastic paraparesis 1
- It does not involve corticospinal tract dysfunction, which is necessary to produce bilateral spastic paraparesis 1
Clinical Evidence Supporting Vitamin B12 Deficiency
- A case report documented a 32-year-old female with sudden onset bilateral lower limb paraparesis and loss of sensation due to vitamin B12 deficiency, who responded fully to vitamin B12 replacement therapy 2
- The American Academy of Neurology recommends spinal MRI to exclude other causes when evaluating myelopathy, as vitamin B12 deficiency must be excluded in the differential diagnosis 1
Additional Causes to Consider in Clinical Practice
- Bilateral cerebral lesions affecting the motor cortex or internal capsule can produce bilateral spastic paraparesis, particularly with parasagittal lesions affecting the leg area of the motor homunculus 1
- Anterior spinal artery syndrome can present with bilateral spastic paraparesis and dissociated sensory deficits 3
- Neurobrucellosis may cause acquired progressive spastic paraparesis 4