The Hoffmann reflex is a specific physical sign assessed during a routine neurological examination to evaluate the central nervous system. This involuntary reflex response is elicited in the hand and provides a quick, low-cost screening tool for potential neurological dysfunction. It is often considered the upper limb equivalent of the Babinski sign, which is tested in the foot. The presence of the Hoffmann reflex suggests an issue within the descending motor pathways that control muscle movement. This reflex is used to check the integrity of the motor system and determine if further testing is warranted.
Eliciting the Reflex: The Testing Procedure
Clinicians employ a precise technique to properly elicit the Hoffmann reflex from a patient. The patient’s hand must be completely relaxed, often held in a partially pronated position with the fingers gently flexed. The examiner supports the patient’s hand and isolates the middle finger, holding it between their own thumb and index finger.
The reflex is then triggered by a sudden, sharp motion aimed at momentarily stretching the finger’s flexor muscles. The examiner achieves this by flicking or snapping the patient’s middle fingernail downward, forcing the distal phalanx into a rapid, momentary flexion.
A “positive” Hoffmann sign occurs if this stimulus causes an involuntary flexion and adduction—a movement toward the palm—of the thumb and, often, the index finger on the same hand. If the thumb and index finger remain still, the test is considered negative. A positive response indicates a hyper-excitable reflex arc, suggesting a loss of normal inhibitory control from the brain.
Understanding the Underlying Physiology
The appearance of a positive Hoffmann reflex is related to a disruption in the body’s motor control system. It is considered a pathological deep tendon reflex resulting from damage to the Upper Motor Neuron (UMN) tract, specifically the corticospinal pathway. UMNs are nerve cells that originate in the brain and travel down through the brainstem and spinal cord, acting as the master control system for voluntary movement.
The primary function of the UMN pathway is to modulate and inhibit the excitability of spinal reflexes, keeping them in check. The Hoffmann reflex itself is a monosynaptic spinal reflex arc, meaning it involves a direct connection between a sensory neuron and a motor neuron in the spinal cord. Normally, the descending UMN signals suppress this inherent reflex arc, preventing it from producing an involuntary movement in response to minor stimuli.
When the UMN pathway is damaged—for instance, by a lesion in the brain or spinal cord—this inhibitory control is lost. The spinal reflex arc is then released from its usual suppression, a phenomenon known as a “release phenomenon.” This loss of inhibition causes the reflex to become hyperactive, leading to the exaggerated, involuntary finger and thumb movements observed in a positive Hoffmann sign.
Clinical Significance of a Positive Result
A positive Hoffmann sign is a finding in a neurological exam that suggests damage to the Upper Motor Neuron pathway, located above the level of the forearm. The reflex arc is primarily situated in the cervical segments of the spinal cord (C5-T1), meaning a positive result points to a lesion in the brain or cervical spine. This finding immediately directs a clinician’s attention toward the central nervous system as the source of the patient’s symptoms.
The sign is crucial in the diagnosis of degenerative conditions affecting the neck, such as cervical spondylotic myelopathy, where the spinal cord is compressed. A positive Hoffmann sign can also support the diagnosis of other neurological diseases involving UMN damage, including multiple sclerosis (MS), stroke, brain or spinal cord tumors, and amyotrophic lateral sclerosis (ALS). The presence of the sign helps to localize the pathological process to the upper motor system.
A positive Hoffmann sign is most concerning when it is unilateral (appearing only on one side of the body) or when it is an acute, new finding. Asymmetry suggests a focal lesion affecting the corticospinal tract. However, the sign can occasionally be found bilaterally in a small percentage of healthy, hyper-reflexive individuals or in those with conditions like hyperthyroidism. Therefore, while a positive Hoffmann sign is a valuable screening tool, it must always be interpreted in conjunction with a patient’s medical history, other clinical findings, and confirmatory neuroimaging tests such as MRI.