Hoffmann's reflex

Hoffmann's reflex, often abbreviated as the Hoffmann sign, is a neurological examination procedure used to assess the integrity of the corticospinal tract, which runs from the brain through the spinal cord. This reflex is named after Johann Hoffmann, a German neurologist who first described it in the early 20th century. The Hoffmann's reflex is considered a deep tendon reflex similar to the knee jerk reflex, but it specifically involves the fingers rather than the legs.

Procedure

To elicit Hoffmann's reflex, the examiner holds the patient's middle finger loosely and flicks the fingernail downward, causing a sudden extension of the finger. A positive Hoffmann's sign is indicated by the involuntary flexion of the thumb and/or index finger in response to this stimulus. This reflex is a sign of hyperreflexia, which can be indicative of an upper motor neuron lesion affecting the corticospinal tract. The presence of Hoffmann's reflex is particularly associated with conditions such as Multiple Sclerosis, Amyotrophic Lateral Sclerosis (ALS), and cervical spinal cord compression.

Clinical Significance

Hoffmann's reflex is an important diagnostic tool in neurology. Its presence or absence can help in the localization of neurological lesions and in distinguishing between upper and lower motor neuron diseases. Upper motor neuron lesions, which can be indicated by a positive Hoffmann's sign, are characterized by increased muscle tone, hyperreflexia, and the presence of pathological reflexes. In contrast, lower motor neuron lesions typically present with muscle weakness, atrophy, fasciculations, and reduced reflexes.

Differential Diagnosis

When a positive Hoffmann's reflex is observed, it is crucial to perform further diagnostic evaluations to determine the underlying cause. Magnetic Resonance Imaging (MRI) of the brain and spinal cord, along with other neurophysiological studies such as Electromyography (EMG) and Nerve Conduction Studies (NCS), can be instrumental in identifying the specific location and nature of the lesion.

Limitations

While Hoffmann's reflex is a useful diagnostic tool, it has its limitations. The reflex can be present in healthy individuals without any neurological disorders, particularly in those with naturally brisk reflexes. Therefore, the interpretation of Hoffmann's reflex should always be considered in the context of other clinical findings and diagnostic tests.

See Also

• Babinski sign
• Clonus
• Deep tendon reflex
• Upper motor neuron
• Lower motor neuron