Muscle twitching, cramp and peripheral nerve hyperexcitability (PNH).

From the outset I would like to establish that Peripheral nerve hyperexcitablity (PNH) can arise due to a number of causes, for example, nerve damage caused by toxins or drugs, or it can have an underlying genetic cause. In addition to this it may also be one the symptoms observed in other neurological disorders. However, in many cases it is acquired and is often immune related, therefore, for the purpose of this site, the term PNH will only apply to this particular type with the added benefit that autoimmune PNH has been the most studied.

Peripheral nerve hyperexcitablity (PNH) is a generalised term that is used to cover a spectrum of disorders that exhibit the symptoms of continuous involuntary muscle fiber activity Over the years a variety of names have been used to describe these symptoms normally based on clinical observations. Some of these descriptive terms include neuromyotonia (NMT), cramp fasciculation syndrome (CFS), benign fasciculation syndrome (BFS), benign cramp fasciculation syndrome (BCFS), continuous muscle fiber activity, continuous motor nerve discharges, Isaacs syndrome, and undulating or generalised myokymia.

However, neuromyotonia, benign fasciculation syndrome and cramp fasciculation syndrome are the most commonly used terms at the time of diagnosis In view of the fact that NMT, CFS and BFS all share similar clinical symptoms and EMG findings and associations with other immune disorders, most noteably myasthenia gravis (MG), they can be considered as slight variants of autoimmune PNH.

The Cause. Research based evidence indicates an autoimmune defect in the form of a potassium channelopathy as the likely cause of PNH. The principle responsibility of the immune system is protecting the body from infection. This protection is provided by circulating antibodies in the bloodstream which are designed to attack foreign matter. Studies of patients with PNH have shown that approximately 40% have a problem with the immune system. This causes antibodies to attack or interfere with a part of the nerve known as the potassium channel. The potassium channel along with the sodium channel are two of the chemical mechanisms within the nerve that are involved in the production of nerve cell signals. When functioning normally these two chemicals are in a form of equilibrium. However, the immune fault destabilises this balance, stimulating the nerve cell into transmitting involuntary impulses that results in muscle fiber activity. Associations with other immune disorders further indicate that peripheral nerve hyperexcitability is an autoimmune dysfunction.

The Effect
The primary effect caused by PNH is involuntary muscle fibre activity in the form of muscle twitches(fasciculations), cramp and cramp like feelings. In turn this may lead to muscular aches, pain, soreness and discomfort. Sensory symptoms (paresthesia) such as pins and needles, numbness, tingling and burning sensations might also be present to a more or lesser degree. Secondary to these, sleep disturbance, fatigue and an intolerance to exercise may also be experienced, though these might not become evident until a period of time after the onset of the main symptoms. All these symptoms can vary in terms of severity with good and bad periods lasting days or months. Normally the twitches are always present while the other symptoms can wax and wane.


The purpose of this site is to give an insight into Peripheral Nerve Hyperexcitability. It is not the intention that it is used as a means of self diagnosis. Always seek professional medical advice on any concerns you may have. The medication I mention will only relate to, and will have been prescribed for me. It is not suggested by me as treatment for anyone else.

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