title: Absent quadriceps reflex with distant toe flexor response: An underrecognized neurological sign.
abstract: As opposed to finger flexion response upon tapping the styloid process with absent brachioradialis reflex (inverted brachioradialis reflex), toe flexion response upon patellar percussion with absent quadriceps reflex is a quite underrecognized neurological sign, and has been reported only once in the literature. Similar to the inverted brachioradialis reflex, this sign can also be useful for neurological localization. We hereby report a patient presenting with signs and symptoms of lumbar radiculopathy in the setting of an anterior epidural mass compressing the cauda equina at L2-L4, without evidence of myelopathy. Upon examination, the patient had bilateral absent quadriceps reflexes with a right toe flexor response when the right patella was percussed. An absent quadriceps reflex with distant toe flexor response is proposed as a lower extremity equivalent of the inverted brachioradialis reflex, likely localizing to L3-L4 levels. Spindle hypersensitivity due to lack of reciprocal inhibition from antagonist muscles is hypothesized as a possible underlying mechanism. Further observations should help clarify the most common underlying etiology (radicular vs. radiculomyelopathy). Neurologists should be able to recognize this sign, as it can be helpful for neurological localization.
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, MN, USA. Electronic address: carvalho.diego@mayo.edu.
authors.forename: Diego Z
authors.initials: DZ
authors.lastname: Carvalho
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Boes
mesh_terms: D006801:Humans; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D009470:Muscle Spindles / Q000503:physiopathology*; D009460:Neurologic Examination / Q000379:methods*; D010329:Patella / Q000502:physiology; D052097:Quadriceps Muscle / Q000503:physiopathology*; D011843:Radiculopathy / Q000175:diagnosis*; D012021:Reflex, Abnormal / Q000502:physiology*; D014034:Toes / Q000502:physiology
keywords: Inverted reflex; Knee reflex; Neurological examination; Radiculopathy; Toe flexion