In Brown-Sequard syndrome at the level of injury, which of the following signs is commonly observed due to LMN involvement?

In Brown-Sequard syndrome at the level of injury, which of the following signs is commonly observed due to LMN involvement?

• A. Lower motor neuron presentation.
• B. Upper motor neuron signs only.
• C. No motor signs.
• D. Pure spasticity without weakness.

Answer: (A)

Brown-Sequard syndrome creates opposite patterns of loss above and below the lesion, with a key difference at the level of injury: the ventral horn cells and ventral roots on the affected side are damaged, producing lower motor neuron-type signs right at that level. This means weakness with reduced or absent reflexes, decreased muscle tone, and sometimes fasciculations or muscle atrophy in muscles served by the damaged segments. Above the lesion, corticospinal tracts are disrupted, so you get upper motor neuron signs, and below the lesion you see UMN signs as well. The combination is what makes the at-the-level finding an LMN presentation. The other options would not fit because spasticity without weakness, or signs limited to UMN features, wouldn’t reflect the local LMN involvement, and no motor signs would be incorrect given the motor tissue damage at the level.

Brown-Sequard syndrome creates opposite patterns of loss above and below the lesion, with a key difference at the level of injury: the ventral horn cells and ventral roots on the affected side are damaged, producing lower motor neuron-type signs right at that level. This means weakness with reduced or absent reflexes, decreased muscle tone, and sometimes fasciculations or muscle atrophy in muscles served by the damaged segments. Above the lesion, corticospinal tracts are disrupted, so you get upper motor neuron signs, and below the lesion you see UMN signs as well. The combination is what makes the at-the-level finding an LMN presentation. The other options would not fit because spasticity without weakness, or signs limited to UMN features, wouldn’t reflect the local LMN involvement, and no motor signs would be incorrect given the motor tissue damage at the level.