Hoffmann’s reflex, often referred to as Hoffmann’s sign, is an involuntary neurological response tested on the fingers during a physical examination. This test evaluates the reflexes of the upper extremities and is also known as the digital reflex or snapping reflex. The primary purpose of eliciting this sign is to screen for potential issues within the central nervous system, specifically involving the pathways that control movement in the upper limbs. The results guide a doctor toward further diagnostic testing.
How the Reflex is Elicited
The test begins with the patient’s hand held in a relaxed position, with the fingers partially bent and the wrist loose. Relaxation is important because tension in the hand muscles can interfere with the true reflex response. The physician isolates the patient’s middle finger, typically holding it near the top joint.
To elicit the reflex, the examiner uses their thumb or index finger to deliver a sharp flick to the patient’s middle fingernail. This action forces the distal part of the finger into a brief, sudden flexion before being released. The mechanical stimulation triggers a reflex arc at the spinal cord level.
In a healthy individual, this maneuver results in no movement or a very minimal reaction in the other fingers. A negative result means the reflex is adequately tempered by the brain’s descending control pathways.
Interpreting a Positive Hoffmann’s Sign
A positive Hoffmann’s sign is visible as an involuntary, quick flexion or twitching of the thumb and the index finger, often making them move toward each other. This complete positive response includes the flexion and adduction of the thumb, coupled with a slight flexion of the index finger. This reflexive movement is known as hyperreflexia, indicating the nervous system has overreacted to the stimulus.
The physiological significance of this exaggerated response lies in its connection to the Upper Motor Neurons (UMNs). UMNs originate in the brain and travel down the spinal cord, forming the corticospinal tract. This tract is responsible for voluntary movement and for suppressing spinal reflexes in adults.
When a positive sign is observed, it suggests damage to these descending UMN pathways, which removes the brain’s inhibitory control over the reflex. The spinal reflex arc then becomes hyperexcitable, causing the exaggerated movement in the thumb and index finger. A strongly active or asymmetrical positive sign is particularly suggestive of a problem with the corticospinal tract.
Conditions Associated with the Sign
A positive Hoffmann’s sign is strongly associated with conditions affecting the cervical spinal cord, where the UMN pathways to the arms are located. The most common correlation is cervical myelopathy, which is spinal cord compression in the neck, often due to degenerative changes like herniated discs or spinal stenosis. This compression disrupts the corticospinal tract, leading to the loss of inhibition.
Other significant neurological disorders that can present with a positive Hoffmann’s sign include multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and stroke impacting the motor cortex. Unilateral positive results are more concerning as they often indicate a focal nervous system injury.
A positive Hoffmann’s sign does not automatically confirm a severe neurological disorder. Approximately three percent of the general population may exhibit a positive sign without underlying spinal cord compression or UMN disease. A positive result can also be temporarily observed in individuals experiencing high anxiety or hyperthyroidism. This finding must always be interpreted by a physician in conjunction with the patient’s other symptoms and confirmed with further diagnostic testing.