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The doctor snaps or flicks the nail of the middle or 4th finger. A
positive finger flexor response elicited in this manner is known as the
Hoffmann reflex or sign.
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The doctor holds the middle finger while partially flexing it between
his/her finger and thumb, then taps or flicks the underside of that
finger. A positive finger flexor response elicited in this manner is
known as the Trömner sign.
What causes the thumb to flex?
The finger flexor response (Hoffmann relex or Trömner sign) is somewhat similar to the Babinski sign in that it is suggestive of a lesion or impingement along the corticospinal tract.What is the corticospinal tract?
Very long nerve axons which originate in the part of the brain called the cerebral cortex travel through the brainstem, cross over at the top of the cervical spine and travel down each side of the spinal cord. This path is the corticospinal tract which is sometimes called the pyramidal tract since the area where the crossover of nerves occurs has a pyramid-like shape.
Corticospinal tract neurons are referred to as “upper motor neurons” but they do not control muscles directly. Neurons in the ventral horn that directly innervate (or stimulate) muscle are called lower motor neurons. It is damage in lower motor neurons which causes atrophy of muscle, while damage in upper motor neurons does not.
How do the Hoffmann or Trömner signs differ from the Babinski sign?
Each of these signs indicate damage in the corticospinal tract. The Babinski sign indicates damage anywhere along the corticospinal tract. However, the Hoffman and Trömner signs are a bit more specific in that they indicate a lesion or damage above the C5 or C6 level of the cervical spine.
Read this post in its entirety:
MS Signs and Symptoms: What is the Hoffmann Reflex?
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