Brisk patellar reflex, weak withdrawal in a dog: where is the lesion?
9-year-old German Shepherd Dog with ambulatory paraparesis and weakness when jumping. Pelvic limbs: bilaterally increased patellar reflex; withdrawal reflex with weak hock and digit flexion but good hip flexion; reduced tone in the caudal thigh muscles; reduced perineal reflex and flaccid tail. Cutaneous trunci reflex and thoracic limbs normal.
What is the most likely neurolocalisation?
chevron_right Show answer and explanation
A. T3–L3, because an increased patellar reflex indicates upper motor neuron disease
In a T3–L3 lesion the withdrawal and perineal reflexes would be normal or increased. Here there are lower motor neuron signs in the sciatic and pudendal territories, which are incompatible with that localisation.
B. L6–S3; the patellar reflex is increased by loss of antagonist muscle tone
Correct. Damage to the sciatic segments or roots reduces the tone of the stifle flexors, which normally dampen extension; the patellar reflex appears exaggerated (pseudohyperreflexia). Hip flexion is preserved because it depends mainly on the iliopsoas, innervated from more cranial lumbar segments.
C. L4–L6, with involvement of the femoral nerve in both pelvic limbs
A lesion of the femoral nerve or its segments reduces or abolishes the patellar reflex and weakens stifle extension. Here the patellar reflex is increased.
D. Multifocal lesion: T3–L3 for the patellar reflex and L6–S3 for withdrawal and perineal
Before proposing a multifocal lesion you should try to explain all the signs with a single lesion. Pseudohyperreflexia explains the increased patellar reflex without needing a second lesion.
lightbulb Key takeaway
Assess the patellar reflex together with the withdrawal, perineal reflex and tail tone: a brisk patellar with weak withdrawal and reduced perineal reflex points to L6–S3 (lumbosacral stenosis, discospondylitis, neoplasia). Always explain the signs with the fewest possible lesions.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.