Definition/Introduction

Westphal’s sign refers to a decreased or absent patellar tendon reflex, also known as the knee-jerk reflex, observed on physical exam. The patellar tendon reflex refers to a kicking-like motion produced by the extension of the knee joint upon the ipsilateral stimulation of the patellar tendon. The reflex is thought to play a role in maintaining balance. The realization of the importance of deep tendon reflexes in the physical exam is often attributed to Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal, who both noted this finding in the late 1800s.[1][2] Westphal’s sign thus receives its name from Carl Friedrich Otto Westphal. The patellar tendon reflex is a deep tendon reflex, similar to the biceps, brachioradialis, triceps, Achilles, and jaw jerk reflexes.[3]

Issues of Concern

Testing for the patellar tendon reflex is a standard part of the physical exam. Abnormal patellar tendon reflexes can indicate neurological disease.[4][5][6][7] In particular, diminished reflex responses are associated with the peripheral nervous system (PNS) disorders, while hyper reflexive responses are related to the central nervous system (CNS) disorders.[8] Therefore, observation of Westphal’s sign would lead to concern for a possible neurological condition, likely affecting the PNS.

Clinical Significance

To understand how an abnormal patellar tendon reflex could indicate a potential neurological disease, it is first useful to review the basic physiology of the patellar tendon reflex. The patellar tendon reflex is elicited by stimulating the patella tendon, classically by a reflex hammer, located inferior to the patella. The stimulation stretches muscle spindles located in the quadriceps muscles, and this muscle spindle stretch excites afferent sensory neurons that innervate the muscle spindles. These afferent sensory neurons then synapse on alpha motor neurons located in the anterior horn area of the spinal cord.[9] The alpha motor neurons then stimulate the quadriceps muscle to contract, producing the reflex response of the quadriceps muscle. The reflex is mediated by the femoral nerve, originating at the L2-L4 level of the spinal cord. It is a monosynaptic reflex because only one synapse produces the reflex response between the afferent sensory neuron and the efferent motor neuron.[10][10]

In addition to synapsing directly with the efferent alpha motor neurons, the afferent sensory neurons make three additional synaptic connections in the spinal cord.[9] One connection is to an inhibitory interneuron. The afferent sensory neurons synapse on these interneurons, which then inhibit alpha motor neurons innervating the hamstring muscles. In this way, the hamstring muscles, antagonists to the contracting quadriceps muscles, relax during the reflex movement. The afferent sensory neurons also communicate with the cerebellum via the dorsal spinocerebellar tracts. The dorsal spinocerebellar tracts carry proprioceptive information to the cerebellum, contributing to the patellar tendon reflexes’ role in maintaining balance. Lastly, the afferent sensory neurons send signals to the cortex.[9]

In general, it is thought that an absent or decreased patellar tendon reflex, as Westphal’s sign describes, is associated with the pathology of the PNS affecting the reflex arc at the level of the spinal cord, while hyperactive reflexes are associated with CNS pathology above the level of the spinal cord mediating the reflex.[1][8][9]

An absent or diminished patellar tendon reflex may be due to PNS pathology affecting either the afferent sensory neurons or the efferent motor neurons. If the reflex is absent or diminished combined with sensory loss, the lesion is likely in the afferent sensory nerves.[9] Examples of diseases that fit this category include sensory polyneuropathies, spinocerebellar degenerations, and root avulsions.[1] If the reflex is absent or diminished in combination with paralysis, muscle atrophy, or fasciculations, the pathology would more likely involve the efferent motor component of the reflex. Examples of diseases that fit this category include motor neuronopathy, radiculopathy, and neuromuscular junction disorders, such as Lambert Eaton syndrome.[1] Many additional causes of peripheral neuropathy can yield an absent or diminished patellar tendon reflex, including diabetes, alcohol use disorder, amyloidosis, vitamin deficiencies, toxins, and remote cancer.[9] Thus the observation of Westphal’s sign carries little specificity but can support the diagnosis of pathology of the PNS.

Observation of a hyperactive patellar tendon reflex, on the other hand, generally suggests pathology to the CNS above the L2-L4 spinal cord level, where the patellar tendon reflex is mediated. The cerebral cortex and regions of the brainstem influence the deep tendon reflexes, such as the patellar tendon reflex.[9] These areas of the brain send connections to the reflex arc via gamma motoneurons, the corticospinal tract, and likely other descending pathways of the spinal cord.[1][9] Insight into the location of the CNS lesion is obtainable by observing deep tendon reflexes in multiple parts of the body. For example, a hyperactive patellar tendon reflex with a normal biceps reflex would suggest pathology in the spinal cord between C5/C6 (where the biceps reflex is mediated) and L2/L4 (where the patellar tendon reflex is mediated).[9][10] Analysis of the same reflex on both sides is also helpful. For example, a hyperactive patellar tendon reflex in the right leg but a normal patellar tendon reflex in the left leg might suggest lateral corticospinal tract pathology on the right side.[9]

Hyperthyroidism and hypothyroidism are also known to affect reflexes such as the patellar tendon reflex. Hyperthyroidism is associated with hyperreflexia and accelerated relaxation of the contracting muscles of the deep tendon reflex.[11][12] Conversely, hypothyroidism is associated with diminished reflexes and delayed relaxation of the contracting muscles of the deep tendon reflex.[13] Therefore, thyroid conditions can be part of the differential diagnosis when observing an abnormal patellar tendon reflex.

The quality of the patellar tendon reflex is a valuable clue in diagnosis. However, the diagnostic sensitivity and specificity for abnormal deep tendon reflexes are reportedly 50% to 70% and 70% to 95%, respectively (less specific with increasing age).[5] It is also known that reflexes are sometimes difficult to stimulate in healthy subjects.[1] Further, there is significant intraobserver and interobserver variability when interpreting the reflexes.[1][5] Thus, due to the overall low sensitivity and specificity associated with observation of abnormal deep tendon reflexes, the quality of the patellar tendon reflex must be interpreted in the context of a patient’s full presentation and should not be relied upon solely as a means of diagnosis.[1][5]

Nursing, Allied Health, and Interprofessional Team Interventions

The patellar tendon reflex is simple to elicit. Thus Westphal’s sign and the quality of the patellar tendon reflex, in general, can be easily checked by anyone on the health care team. A technique called the Jendrassik maneuver can be helpful when having difficulty eliciting a patellar tendon reflex in a patient.[9] The maneuver involves eliciting the patellar tendon reflex while the patient clenches their hands and pulls them apart.[14][15][16] The mechanism explaining why this helps elicit deep tendon reflexes is unclear, but it can be a useful maneuver in the clinical setting.[14]

Nursing, Allied Health, and Interprofessional Team Monitoring

Members of the health care team should be cognizant of how an abnormal patellar tendon reflex may be associated with certain neurological conditions. If an examiner observes an abnormal reflex or changes in the quality of the reflex, the health care team may consider further evaluation based on the specific clinical context.