The sign of Lhermitte refers to an electric sensation that goes down the back and the legs when flexing the neck. This can happen for several reasons. A reader of the blog suffered severe trauma to the neck with multiple fractures that were involved. During his recovery he began to feel an electric sensation in the back when it flexed the neck, that is to say, when it carried the head forward. What was happening to him?
What feelings do we have with the sign of Lhermitte?
In certain neck movements, typically in flexion, a cramp is produced and lowered through the spine. Sometimes the sensation also goes down by the legs and even by the arms and the trunk. This sign was first described at the beginning of the last century in patients with multiple sclerosis, although there are other causes, as we will see later.
Although neck flexion is the typical recognized gesture, it can occur in other movements when there is some structure that compresses the marrow. In these cases, by extending the neck (carrying the head back), or more rarely in rotations, this phenomenon can be triggered.
Why does the sign of Lhermitte occur?
In the posterior area of the medulla (posterior cords), nerve fibers carry sensitive information. In some lesions the myelin layer that overlies these nerves will be lost. This makes them very sensitive and hyperexcitable and when the gesture of flexing the neck is triggered the electric discharge that runs the back.
The cause is not always so clear. There are cases of trauma that affect the neck that in the recovery period present the sign of Lhermitte without being able to demonstrate the presence of a demyelination in the posterior cords. In these cases it is usual to yield with the passage of the weeks.
What situations cause the sign of Lhermitte?
– The sign of Lhermitte is typical of a cervical demyelinating lesion in the context of multiple sclerosis.
– In cervical trauma, typically with fractures, without appreciable involvement of the marrow, you can see this sign without being clear the mechanism that produces it. It is assumed that there will have been a contusion of the marrow but in many cases it is not able to demonstrate. It is common for it to appear several weeks after the trauma. The cases that have been published in the medical literature yield in a period of between 4 months and a year.
– In wear injuries such as osteoarthritis, the space of the spinal cord can be compromised. Gestures such as cervical extension can cause compression of the cord and trigger the cramp. This is what we call the inverted Lhermitte.
– Coughing, sneezing, or pushing (Valsalva maneuver) may produce this sign in people who have compromised the normal flow of cerebrospinal fluid.
– Deficiency of vitamin B12 can cause an affectation of the posterior cords and therefore give this sign. When there is sensitive symptomatology without its origin being clear, it is important to look at the levels of this vitamin in a blood test.
– Radiation therapy or cisplatin used in chemotherapy may cause the appearance of the sign of Lhermitte.
– There are other more rare causes like some rheumatic diseases or tumors that affect the marrow that also can produce it.
Returning to the case of our reader, it is probable that in the accident suffered an injury in the back of the marrow. The normal thing is that with the passage of the months this sensation disappears to him.