Question

The following conditions may present with both upper and lower motor neuron involvement EXCEPT

• A. Subacute combined degeneration of spinal cord
• B. Friedreich's ataxia
• C. Amyotrophic lateral sclerosis
• D. Becker's Dystrophy

Hint:

Three of these damage the nervous system itself; one is a disease of muscle fiber alone.

Answer 1

The Correct Option is D

This question asks which of four conditions is the exception that does not show both upper and lower motor neuron signs together.

1. Subacute combined degeneration of spinal cord: Vitamin B12 deficiency here damages both the corticospinal tracts and peripheral nerves, giving a true combined picture.
2. Friedreich's ataxia: This damages the corticospinal tracts along with the dorsal root ganglia, producing extensor plantars together with absent reflexes.
3. Amyotrophic lateral sclerosis: This disease directly destroys both upper and lower motor neurons simultaneously, making combined signs its hallmark feature.
4. Becker's Dystrophy: This is a primary muscle fiber disease from partly functioning dystrophin, with no damage to the motor neurons or corticospinal tracts, so it shows pure muscle-type weakness without true upper motor neuron signs.

Since Becker's Dystrophy is purely a muscle disease rather than a nervous system disease, it is the exception here.

Let's summarize:

• SACD, Friedreich's ataxia, and ALS all damage both upper and lower motor neuron pathways.
• Becker's Dystrophy is a pure muscle disease and does not involve the motor neurons at all.

So the exception is Becker's Dystrophy.