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What is Lhermitte's phenomenon?
Lhermitte's phenomenon is a sudden, electric shock-like feeling that goes from the neck down the back when you bend your head forward. In some people, the feeling also continues into the arms or legs. It usually only lasts a few seconds, but can still be unpleasant and cause concern because it often comes on completely unexpectedly.
Many people describe it as feeling like it "rushes like electricity" when they look down at their mobile phone, tie their shoes or cough. Lhermitte's phenomenon is not a disease in itself, but a neurological symptom that suggests an impact on the nerve pathways in the cervical spine of the spinal cord, especially the posterior nerve cords.
What does Lhermitte's phenomenon feel like?
Typically, the discomfort is triggered when the neck is bent forward. The feeling comes on quickly, is short-lived and can be repeated several times in the same day. For some it hurts, while others mostly experience a tingling, vibrating or strange sensation.
A common example is that the feeling comes when bending over the sink, looking down at a computer or sneezing. It is typical that it passes in seconds, but if the episodes recur, the cause should be assessed medically.
Causes of Lhermitte's phenomenon
The underlying mechanism is usually that nerve fibers in the cervical spinal cord have become irritated or damaged. Often it is a matter of demyelination, i.e. that the myelin has been damaged. Myelin is the insulating protective covering of the nerve and is needed for nerve signals to be conducted normally. When it is damaged, a simple neck movement can trigger an incorrect "discharge" in the nervous system.
Lhermitte's phenomenon is often associated with multiple sclerosis, but there are several other causes. It can also be seen in changes in the cervical spine with pressure on the spinal cord, after radiation therapy or chemotherapy, in inflammation of the spinal cord and in vitamin B12 deficiency.
When can vitamin B12 deficiency be the explanation?
Vitamin B12 deficiency is a particularly important cause because it can sometimes be fully treated if detected in time. The deficiency can damage the posterior cords of the spinal cord and cause neurological symptoms such as numbness, balance difficulties, gait impairment and, in more rare cases, Lhermitte's phenomenon. There may be neurological effects even without clear anemia.
The suspicion becomes stronger if you also have fatigue, tingling in the hands or feet, impaired vibration sense or risk factors such as a vegan diet without supplements, intestinal disease, previous stomach surgery or use of nitrous oxide. In this case, blood tests are often a reasonable part of the investigation.
When should you seek medical attention?
Lhermitte's phenomenon is usually not dangerous in itself, but it should not be dismissed if it is new. Seek medical attention if you experience recurring electric shocks from the neck down to the back, especially if you also have numbness, weakness, difficulty walking, balance problems or bladder dysfunction. In this case, you need to rule out effects on the spinal cord.
If the symptom is accompanied by rapidly increasing neurological symptoms, the assessment should be carried out urgently. The same applies if you have known cancer, recent trauma to the neck or other signs of pronounced B12 deficiency or inflammatory nerve disease.
The investigation is usually based on medical history, neurological examination and sometimes MRI of the brain or cervical spine. Blood tests may be needed to find treatable causes such as vitamin B12 deficiency or other nutritional disorders. There is no single test that “proves” Lhermitte’s phenomenon, but the goal is to find the cause behind the symptom.
Treatment of Lhermitte’s phenomenon
Treatment is directed at the root cause. If the symptoms are due to multiple sclerosis, inflammation, pressure on the spinal cord or B12 deficiency, that condition needs to be treated. When the cause is addressed, the symptom often decreases or disappears completely.
Lhermitte’s phenomenon is therefore a symptom that can indicate an underlying chronic neurological disease, or sometimes a treatable deficiency or mechanical impact that can be detected before major nerve damage has time to develop. That is why early medical assessment is important in order to be able to plan the investigation in a structured way.
Do you want to know if fatigue or numbness can be related to, for example, vitamin B12 deficiency or other abnormal values? Order a health check up from the Testmottagningen and get a clear basis for the next step.
