The Hoffman sign is a neurological reflex test used to assess the integrity of the central nervous system, particularly the corticospinal tract. This tract is the main pathway responsible for carrying motor information from the brain to the spinal cord, controlling voluntary movement. The test is a rapid, non-invasive method to determine if an exaggerated reflex response in the upper limbs signals a loss of normal inhibitory control. A positive result prompts a thorough investigation into the patient’s neurological health.
Eliciting the Hoffman Sign
The Hoffman sign is elicited during a routine neurological examination. The patient holds out their hand, allowing it to relax completely, often with the wrist slightly extended. The clinician cradles the hand for support and focuses on the patient’s middle finger, holding it loosely at the proximal interphalangeal joint. The clinician then performs a swift, forceful flick or snap on the nail of the middle or ring finger, forcing the distal phalanx into sudden flexion, which stretches the finger flexor muscles and tendons. The clinician observes the thumb and index finger for any involuntary movement immediately following the flick.
Interpreting the Results
A positive Hoffman sign occurs when the flicking action causes involuntary, quick flexion and adduction (moving toward the palm) of the thumb, often accompanied by slight flexion of the index finger. This response is hyperreflexia, meaning the reflex arc is overactive. A positive sign implies the presence of an Upper Motor Neuron (UMN) lesion, indicating damage to the descending motor pathways from the brain or spinal cord. The corticospinal tract normally maintains inhibitory control over spinal reflexes. When this control is lost due to a UMN lesion, the reflex becomes exaggerated.
A negative result means there is no involuntary movement, suggesting inhibitory control is intact. A positive sign is not always pathological; up to 3% of healthy individuals may exhibit a response, especially if they are generally hyper-reflexive or anxious. For the sign to be clinically significant, it is usually markedly active, present on only one side (asymmetrical), or occurs alongside other signs of neurological dysfunction. The sign must be interpreted within the context of a complete neurological examination.
Clinical Significance and Associated Conditions
A positive Hoffman sign helps a clinician localize a neurological problem to the central nervous system above the level of the reflex arc. Since the finger flexor reflex arc is located in the cervical spinal cord, a positive sign points to a lesion in the brain or the cervical spinal cord itself. Diagnosis in this region typically requires a magnetic resonance imaging (MRI) scan. The most frequent condition associated with a positive Hoffman sign is cervical myelopathy, which is spinal cord compression in the neck, often caused by degenerative changes like cervical spondylosis. The compression damages the descending motor tracts, leading to the loss of inhibition and the pathological reflex.
The sign’s presence is often an early indicator of compression, prompting further diagnostic testing. A positive sign can also be a finding in other central nervous system diseases, including multiple sclerosis (MS) and stroke, especially if the motor pathways are affected. While the sign is highly specific for pathology when asymmetrical, its absence does not rule out cervical myelopathy. Less common causes, such as brain tumors, severe anxiety, or hyperthyroidism, can also lead to a positive sign due to heightened nervous system excitability.
Distinguishing Hoffman’s from Related Reflexes
The Hoffman sign is often considered the upper limb counterpart to the Babinski sign, both screening for UMN lesions. The Babinski sign is elicited by stroking the sole of the foot, resulting in the big toe moving upward (extension) and the other toes fanning out. Both reflexes indicate a loss of inhibition from the corticospinal tract but are tested on different body parts.
The Trömner sign is a similar finger flexor reflex, differing primarily in the method of stimulation. The Trömner sign is elicited by tapping the palmar surface of the middle finger’s distal phalanx. The resulting response—flexion of the thumb and other fingers—is functionally identical to the Hoffman sign. Both tests check for the same hyper-reflexive response in the upper extremity and indicate pyramidal tract dysfunction above the cervical spinal cord.