The Hoffman sign is a simple, non-invasive neurological test used to screen for potential issues within the central nervous system. This assessment checks the integrity of the corticospinal pathways, which control voluntary movement in the upper body. A positive reaction suggests an abnormality in these pathways. The sign quickly identifies hyperexcitability in the reflex arc, pointing toward an underlying condition requiring further investigation.
How the Hoffman Sign is Tested
The examination for the Hoffman sign is a straightforward procedure that requires no specialized equipment, relying only on the physician’s hands and observation. The patient is asked to hold their hand out and let it completely relax, often with the fingers slightly flexed.
The core of the test involves the physician quickly “flicking” or snapping the nail of the middle finger downward. This action creates a sudden, passive stretch of the flexor tendons in the patient’s finger. A positive result occurs when this stimulus causes an involuntary, rapid movement in the patient’s thumb and index finger. Specifically, the thumb flexes and moves inward (adducts), while the index finger also flexes toward the thumb in a motion known as opposition.
The test is often performed on both hands to ensure the reaction is consistent and to compare responses between the left and right sides. If the thumb and index finger do not move in response to the flick, the result is considered a negative Hoffman sign. This provides immediate clinical information that helps direct the next steps in a neurological evaluation.
The Neurological Mechanism of a Positive Result
A positive Hoffman sign indicates dysfunction within the body’s Upper Motor Neuron (UMN) system. UMNs originate in the brain’s motor cortex and travel down the spinal cord, forming descending pathways like the corticospinal tract. The primary function of this pathway is to modulate and inhibit the lower spinal reflexes.
When damage occurs along the corticospinal tract, inhibitory control is lost. The loss of descending inhibition causes lower spinal motor neurons to become hyperexcitable. The passive stretching of the finger tendons during the test acts as a mechanical stimulus, triggering a hyperactive stretch reflex because the UMN “brake” is no longer functioning.
This overreaction causes the involuntary flexion of the thumb and index finger observed in a positive sign. The presence of this hyperreflexia suggests the problem lies above the spinal cord segment controlling the hand muscles, typically in the cervical spine or the brain. The sign indicates that the central nervous system has lost its ability to temper the reflex response.
Conditions Associated with a Positive Hoffman Sign
The clinical significance of a positive Hoffman sign lies in its association with pathology affecting the central nervous system. The most frequent cause is cervical myelopathy, which results from spinal cord compression in the neck region. This condition is often caused by degenerative changes like osteoarthritis or disc herniation that narrow the spinal canal. This narrowing places pressure directly on the corticospinal tract, creating the UMN lesion that manifests as the positive reflex.
The sign can also be observed in other serious neurological disorders that cause widespread demyelination or tissue damage. These include Multiple Sclerosis (MS), where the immune system attacks the protective myelin sheath. A stroke or a brain or spinal cord tumor can also damage the UMN pathways, resulting in the same hyperactive reflex. Amyotrophic Lateral Sclerosis (ALS), a progressive neurodegenerative disease, commonly produces a positive sign as it causes the degeneration of both upper and lower motor neurons.
The Hoffman sign is not a definitive diagnosis and can occasionally be observed in healthy people, sometimes referred to as a “false positive.” Approximately three percent of the population may naturally exhibit this reflex without pathological cause. Non-neurological conditions like hyperthyroidism or severe anxiety can also mimic a positive sign due to increased bodily reflexivity. Therefore, while a positive result warrants further investigation, it must always be interpreted by a specialist in the context of a patient’s full history and symptoms.