Reflex Abnormalities

Reflex Physiology

Reflexes are used for examination purposes, but they demonstrate integral and sometimes complex functioning of the nervous system. Reflexes can be physiologic and pathologic. Physiologic reflexes use pathways that are normally functioning in a patient of the particular age and state. Pathologic reflexes are abnormalities that can be either errors within the reflex pathway or inappropriate responses for the age and state of the patient.

Tendon reflexes are elicited by using a combination of percussion and limb positioning to transiently lengthen a tendon. Contraction of the muscle is the normal response. Tendon reflexes are elicited with a certain character and strength in individuals with normal neurologic functioning. The reflex loops that serve these are used normally for precise control over movement.

If there is damage to the corticospinal tract innervating these fibers, then the affected tendon reflexes are reduced acutely because of loss of descending input and then become enhanced because of increased function of the segmental reflex pathways. This results in hyperreflexia with an enhanced response; if severe, clonus is elicited by the reflex. When reflexes are so enhanced, there is also activation of muscles not usually affected by the tendon reflex (i.e., generalization).

Damage to the sensory afferents serving the reflex will result in reduced reflex because of a reduction in the amplitude and synchrony of the afferent signal. Damage to the motor efferents will produce reduced reflex. Distinguishing motor versus sensory defect can be difficult. In general, with a sensory deficit, motor power should be normal; with a motor nerve defect, motor power will be reduced.

Frontal release signs are reflexes that are normally present in infants but are abolished in normal adults. In the presence of significant cerebral damage, especially frontal, they can recur and hence are sometimes termed frontal release signs. Glabellar, palmomental, snout, and grasp are the most common frontal release signs. Rooting is less common and less reliable but is discussed.

The Romberg test examines stability of stance and is essentially a test of proprioception. As such, it examines integrity of the dorsal columns. Cerebellar lesions will affect stance even when the patient has their eyes open.

Localization and Diagnosis of Reflex Findings