Question

A middle aged male presented with sub acute paresthesias in hands and feet, loss of vibration and position sense and a progressive spastic and ataxic weakness. Examination revealed loss of reflexes along with presence of Babinski sign. Investigation revealed presence of macrocytic RBCs and elevated serum homocystine levels. The most likely diagnosis is

• A. \( \text{Tabes dorsalis} \)
• B. \( \text{Hereditary spastic paraplegia} \)
• C. \( \text{Subacute combined degeneration of spinal cord} \)
• D. \( \text{Spondylotic myelopathy} \)

Hint:

\textbf{Neurology: Subacute Combined Degeneration.} Remember that SCD is a consequence of vitamin B12 deficiency affecting the posterior and lateral columns of the spinal cord and peripheral nerves. The clinical picture often includes sensory ataxia, spasticity, and peripheral neuropathy, frequently accompanied by macrocytic anaemia.

Answer 1

The Correct Option is C

The clinical presentation described includes a combination of neurological findings that point towards a specific condition: **Subacute paresthesias in hands and feet, loss of vibration and position sense:** These are characteristic features of posterior column dysfunction in the spinal cord. **Progressive spastic and ataxic weakness:** This suggests involvement of both the corticospinal tracts (leading to spasticity) and the spinocerebellar tracts (leading to ataxia). **Loss of reflexes along with the presence of Babinski sign:** Loss of reflexes (areflexia) is often seen with peripheral neuropathy or in the acute phase of spinal cord injury, while a positive Babinski sign indicates upper motor neuron involvement. The combination here is somewhat unusual but can be seen in subacute combined degeneration affecting both central and peripheral nervous systems. **Macrocytic RBCs and elevated serum homocystine levels:** Macrocytic anaemia suggests vitamin B12 or folate deficiency. Elevated homocystine levels can occur in both B12 and folate deficiency, as these vitamins are cofactors in the metabolism of homocysteine. Considering these findings together, the most likely diagnosis is Subacute combined degeneration of spinal cord (SCD). SCD is a neurological disorder caused by vitamin B12 deficiency, leading to demyelination of the posterior and lateral columns of the spinal cord, as well as peripheral nerves. The macrocytic anaemia and elevated homocystine levels strongly support this diagnosis. Let's briefly consider why the other options are less likely: **Tabes dorsalis:** This is a late manifestation of syphilis affecting the posterior columns and dorsal roots, leading to sensory ataxia, lancinating pains, and Argyll Robertson pupils. While it involves the posterior columns, the other features, particularly the macrocytic anaemia and elevated homocystine, are not typical. **Hereditary spastic paraplegia:** This is a group of inherited disorders primarily affecting the corticospinal tracts, leading to progressive spasticity of the lower limbs. Sensory loss and macrocytic anaemia are not typical features. **Spondylotic myelopathy:** This is caused by degenerative changes in the cervical spine leading to compression of the spinal cord. While it can cause spastic weakness and sensory changes, macrocytic anaemia and elevated homocystine are not associated. Therefore, the combination of neurological deficits affecting multiple spinal cord tracts, peripheral nerves, along with macrocytic anaemia and elevated homocystine, strongly suggests subacute combined degeneration of the spinal cord due to vitamin B12 deficiency.