(See also Introduction to the Neurologic Examination.)
Deep tendon reflexes
Deep tendon (muscle stretch) reflex testing evaluates afferent nerves, synaptic connections within the spinal cord, motor nerves, and descending motor pathways. Lower motor neuron lesions (eg, affecting the anterior horn cell, spinal root, or peripheral nerve) depress reflexes; upper motor neuron lesions (ie, non–basal ganglia disorders anywhere above the anterior horn cell) increase reflexes.
Reflexes tested include the following:
Biceps (innervated by C5 and C6)
Radial brachialis (by C6)
Triceps (by C7)
Distal finger flexors (by C8)
Quadriceps knee jerk (by L4)
Ankle jerk (by S1)
Jaw jerk (by the 5th cranial nerve)
Any asymmetric increase or depression is noted. Jendrassik maneuver can be used to augment hypoactive reflexes: The patient locks the hands together and pulls vigorously apart as a tendon in the lower extremity is tapped. Alternatively, the patient can push the knees together against each other, while the upper limb tendon is tested.
Pathologic reflexes
Pathologic reflexes (eg, Babinski, Chaddock, Oppenheim, snout, rooting, grasp) are reversions to primitive responses and indicate loss of cortical inhibition.
Babinski, Chaddock, and Oppenheim reflexes all evaluate the plantar response. The normal reflex response is flexion of the great toe. An abnormal response is slower and consists of extension of the great toe with fanning of the other toes and often knee and hip flexion. This reaction is of spinal reflex origin and indicates spinal disinhibition due to an upper motor neuron lesion.
For Babinski reflex, the lateral sole of the foot is firmly stroked from the heel to the ball of the foot with a tongue blade or end of a reflex hammer. The stimulus must be noxious but not injurious; stroking should not veer too medially, or it may inadvertently induce a primitive grasp reflex. In sensitive patients, the reflex response may be masked by quick voluntary withdrawal of the foot, which is not a problem in Chaddock or Oppenheim reflex testing.
For Chaddock reflex, the lateral foot, from lateral malleolus to small toe, is stroked with a blunt instrument.
For the Oppenheim reflex, the anterior tibia, from just below the patella to the foot, is firmly stroked with a knuckle. The Oppenheim test may be used with the Babinski test or the Chaddock test to make withdrawal less likely.
The snout reflex is present if tapping a tongue blade across the lips causes pursing of the lips.
The rooting reflex is present if stroking the lateral upper lip causes movement of the mouth toward the stimulus.
The grasp reflex is present if gently stroking the palm of the patient’s hand causes the fingers to flex and grasp the examiner’s finger.
The palmomental reflex is present if stroking the palm of the hand causes contraction of the ipsilateral mentalis muscle of the lower lip.
Hoffmann sign is present if flicking down on the nail on the 3rd or 4th finger elicits involuntary flexion of the distal phalanx of the thumb and index finger.
Tromner sign is similar to the Hoffman sign, but the finger is flicked upward.
For the glabellar sign, the forehead is tapped to induce blinking; normally, each of the first 5 taps induces a single blink, then the reflex fatigues. Blinking persists in patients with diffuse cerebral dysfunction.
Other reflexes
Testing for clonus (rhythmic, rapid alternation of muscle contraction and relaxation caused by sudden, passive tendon stretching) is done by rapid dorsiflexion of the foot at the ankle. Sustained clonus indicates an upper motor neuron disorder.
The superficial abdominal reflex is elicited by lightly stroking the 4 quadrants of the abdomen near the umbilicus with a wooden cotton applicator stick or similar tool. The normal response is contraction of the abdominal muscles causing the umbilicus to move toward the area being stroked. Stroking the skin toward the umbilicus is recommended to rule out the possibility that movement was caused by the skin being dragged by the stroking. Depression of this reflex may be due to a central lesion, obesity, or lax skeletal muscles (eg, after pregnancy); its absence may indicate spinal cord injury.
Sphincteric reflexes may be tested during the rectal examination. To test sphincteric tone (S2 to S4 nerve root levels), the examiner inserts a gloved finger into the rectum and asks the patient to squeeze it. Alternatively, the perianal region is touched lightly with a cotton wisp; the normal response is contraction of the external anal sphincter (anal wink reflex). Rectal tone typically becomes lax in patients with acute spinal cord injury or cauda equine syndrome.
For the bulbospongiosus reflex, which tests S2 to S4 levels, the dorsum of the penis is tapped; normal response is contraction of the bulbospongiosus muscle.
For the cremasteric reflex, which tests the L2 level, the medial thigh 7.6 cm (3 in) below the inguinal crease is stroked upward; normal response is elevation of the ipsilateral testis.
