The Hoffmann sign is a specific neurological reflex test used to assess the functioning of the central nervous system, particularly the spinal cord and brain. This quick, equipment-free examination checks for signs of hyperreflexia in the upper extremities. Named after German neurologist Johann Hoffmann, it is a standard component of a comprehensive neurological examination, offering a preliminary indication of potential underlying issues.
The Test: How Hoffman’s Sign is Elicited
The physical maneuver to elicit the Hoffmann sign is straightforward and requires no special tools. The patient is instructed to relax their hand completely, allowing the fingers to be slightly bent. The examiner supports the patient’s hand and wrist, ensuring the muscles are loose.
The examiner grasps the patient’s middle finger near the top joint. A sharp, quick flick is applied to the fingernail or the distal phalanx, forcing a sudden, brief flexion followed by an immediate release. This action momentarily stretches the flexor tendons. The physician watches closely for any involuntary movement in the other fingers, which indicates the result.
Interpreting the Results: What a Positive Sign Means
A positive Hoffmann sign is characterized by an involuntary, rapid flexion and adduction of the thumb, often accompanied by a slight flexion of the index finger. This movement occurs immediately after the middle finger is flicked. A positive result is considered an abnormal finding, suggesting a state of hyperreflexia.
This hyperreflexia indicates dysfunction within the upper motor neuron (UMN) pathway, specifically the corticospinal tract. When this pathway is damaged or compressed, its inhibitory control over the spinal reflexes is reduced.
The resulting lack of inhibition causes the spinal reflex arc to become over-excitable. The sudden stretch of the finger flexor muscles triggers an exaggerated reflex contraction in the thumb and index finger. The Hoffmann sign is often considered the upper limb equivalent of the Babinski sign, pointing to a central nervous system abnormality.
Clinical Importance: Conditions Associated with a Positive Sign
While a positive Hoffmann sign suggests an issue with the central nervous system, it is not a stand-alone diagnostic tool. It is a screening test that warrants further investigation, especially when a patient reports other neurological symptoms. The most common association is cervical myelopathy, which is dysfunction of the spinal cord in the neck region, often due to compression from degenerative changes.
The sign can also be a finding in other conditions that affect the UMN pathway, such as multiple sclerosis (MS). Tumors or lesions affecting the brain or spinal cord can also disrupt the corticospinal tract. Furthermore, certain metabolic conditions, including severe vitamin B12 deficiency or hyperthyroidism, have been known to cause hyperactive reflexes and a positive sign.
Interpreting Laterality
It is important to note whether the sign is present on one side (unilateral) or both sides (bilateral). A unilateral positive sign is generally more concerning, as it suggests a focal lesion affecting only one side of the nervous system. A bilateral positive sign may indicate a more diffuse disease process, but it is also observed in healthy individuals who naturally have hyperactive reflexes.
Up to 3% of the general population may have a positive Hoffmann sign without evidence of disease. Physicians interpret the sign alongside the patient’s full medical history and other neurological findings, often confirming suspicions with imaging studies like Magnetic Resonance Imaging (MRI). The sign is most significant when it is notably asymmetrical or associated with other symptoms of neurological decline.