Upper or lower motor neuron signs: telling them apart in the dog
7-year-old crossbred dog with pelvic limb paresis for 3 weeks. Before localising the lesion you want to know whether the signs in those limbs are upper or lower motor neuron.
Which combination of findings indicates a lower motor neuron lesion?
chevron_right Show answer and explanation
A. Increased muscle tone, increased spinal reflexes and mild, late-onset atrophy
This is the upper motor neuron pattern: with loss of descending inhibition, the reflex arc remains intact and disinhibited. Atrophy is only from disuse, mild and slow.
B. Reduced muscle tone, reduced or absent spinal reflexes and marked, early muscle atrophy
Correct. The lower motor neuron (cell body in the ventral horn, root, nerve) is part of the reflex arc: when damaged, tone and reflexes are lost and neurogenic atrophy appears within 1-2 weeks.
C. Paresis with abnormal postural reactions
Both occur in upper and lower motor neuron lesions alike, so they do not help to tell them apart.
D. Incontinence with a distended bladder that is difficult to express
A tense bladder that is difficult to express is typical of upper motor neuron lesions (cranial to S1). In lower motor neuron lesions the bladder is flaccid and easily expressed.
lightbulb Key takeaway
Upper motor neuron: normal or increased tone and reflexes, mild disuse atrophy, bladder difficult to express. Lower motor neuron: reduced or absent tone and reflexes, rapid neurogenic atrophy, flaccid bladder. Lower motor neuron signs localise to the intumescences (C6-T2, L4-S3), roots, nerves, neuromuscular junction or muscle.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.