Absent quadriceps reflex with distant toe flexor response: An underrecognized neurological sign

Area of Science:

• Neurology
• Neuroscience
• Clinical Neurology

Background:

• The inverted brachioradialis reflex (finger flexion with absent brachioradialis reflex) is an established neurological sign.
• A similar reflex involving the lower extremities, the toe flexion response upon patellar percussion with an absent quadriceps reflex, is underrecognized.

Observation:

• A patient presented with lumbar radiculopathy symptoms due to an anterior epidural mass compressing the cauda equina.
• The patient exhibited bilateral absent quadriceps reflexes and a distinct toe flexor response on the right upon percussion of the right patella.

Findings:

• The observed absent quadriceps reflex with a distant toe flexor response is proposed as a lower extremity equivalent of the inverted brachioradialis reflex.
• This sign is hypothesized to localize neurological deficits to the L3-L4 spinal levels.
• Spindle hypersensitivity, potentially due to reduced reciprocal inhibition from antagonist muscles, is the proposed underlying mechanism.

Implications:

• This sign can be a valuable tool for neurological localization in cases of lumbar radiculopathy.
• Further research is needed to determine the common etiologies, such as radicular or radiculomyelopathy.
• Clinicians should be aware of this sign for improved diagnostic accuracy in neurological assessments.