What is myokymia?
Myokymia refers to a group of conditions that are characterized by continuous, involuntary muscular movements. The slow and uncontrolled muscular movements in myokymia may or may not be visible on the surface of the skin, depending on the type of muscles involved and the amount of subcutaneous fat in the affected region. In the instances where these movements are visible, the surface of the skin ripples continuously in a worm-like movement.
In fact, this peculiar motion makes some affected individuals believe that there may be a worm under the skin. The muscular movements in myokymia occur during rest (such as during sleep). Myokymia is a rare condition that affects individuals with a variety of different neurological and other medical conditions. Under some conditions (such as after exercise), healthy individuals may also display myokymia. However, myokymia is not a life-threatening condition, and is harmless in most instances.
Types of Myokymia
Based on the affected muscle groups, myokymia is generally classified into four broad categories. These include the following:
- Facial myokymia: Facial myokymia affects the muscles of the face.
- Eyelid myokymia: Eyelid myokymia affects the muscles that control the movements of the eyelids.
- Focal myokymia: Also known as segmental myokymia, focal myokymia is restricted to the muscles in one specific region of the body.
- Generalized myokymia: Generalized myokymia affects the muscles in multiple regions of the body, either one after the other or all at the same time.
Signs and Symptoms
Muscular movements are controlled through signals from the motor neurons, whereas sensations are elicited through sensory neurons. Myokymia mostly affects the motor neurons, and causes a variety of signs and symptoms related to muscular movements. Sensory neurons are rarely affected. The following are the general symptoms that are commonly seen in all types of myokymia:
- Twitching of muscle fibers
- Pain in the affected muscles
- Muscle cramps
- Stiffness in the muscles or joints
- Muscular weakness
Read more on benign fasiculation syndrome.
There are other signs and symptoms that are specific to particular types of myokymia. The following are some of the peculiar signs and symptoms of various types of myokymia.
Facial myokymia: In facial myokymia, the muscles on the surface of the face become weak and display slow worm-like movements. However, these involuntary movements do not affect the voluntary movements of the facial muscles.
Eyelid myokymia: Eyelid myokymia is characterized by involuntary twitching movements of the muscles in the eyelids (especially the lower eyelid). The vision in one eye may appear to be shaky, tilted or vertical, resulting in a trembling sensation. The signs and symptoms of eyelid myokymia tend to appear and disappear suddenly.
Focal myokymia: The signs and symptoms of focal myokymia are restricted to specific regions of the body. The muscles of the hands and feet are most commonly involved in focal or segmental myokymia.
Generalized myokymia: Generalized myokymia affects muscles in multiple parts of the body. The affected muscles show involuntary movements, stiffness, and weakness. The associated tendons may display a decreased reflex response. Excessive sweating may also occur. It is important to note that generalized myokymia does not affect the functioning of the involuntary smooth muscles of the body (such as the heart muscles). In addition, no sensory symptoms are evident in this condition.
Read more on lip twitching.
Diagnosis of Myokymia
In addition to the above mentioned signs and symptoms, the diagnosis of myokymia depends on the outcome of a variety of laboratory and clinical tests. The following tests are frequently used in the diagnosis of myokymia:
- Laboratory tests: Body fluids such as urine, blood and cerebrospinal fluid are tested in a clinical laboratory to determine complete blood count, creatine kinase levels, thyroid hormone levels, and the presence of toxins, alcohol and infections.
- Imaging studies: Presence of tumors or any other tissue damage in various parts of the body can be identified through imaging studies such as magnetic resonance imaging (commonly abbreviated as MRI) and computerized tomography (commonly abbreviated as CT scans).
- Nerve conduction velocity test: Nerve conduction velocity is determined in order to test the functional integrity of the nerves. The nerve conduction velocity is slower than normal in case of damaged nerves. Conditions that can result in reduced nerve conduction velocity include demyelination and neuropathies.
- Electromyography: Electromyography is a test to measure the functioning of the muscles and their innervating nerves. An electromyogram is usually conducted along with the nerve conduction velocity test. These tests can detect myokymic muscle activity.
Causes of Myokymia
The movements of muscles in the body are controlled through the action of various nerves that emanate from the brain and the spinal cord. A single nerve can innervate multiple muscles and coordinate their contractions and relaxations. In myokymia, skeletal muscles of the body undergo involuntary contractions.
Transient contractions may be seen in the calf and hand muscles even in normal individuals, especially after bouts of strenuous exercise. Although the exact mechanisms are unclear, myokymic contractions are thought to result from damage to the nerves or the myelin sheaths that surround the nerves.
Persistent myokymia may occur due to the following reasons:
- Facial myokymia: Facial myokymia is one of the most common type of myokymia. Potential causes of facial myokymia include nerve demyelination, brain damage, and tumors in the brainstem. Facial myokymia could also result from Guillain-Barre´ syndrome. Individuals who have undergone radiotherapy in the past may also show signs of facial myokymia.
- Eyelid myokymia: The superior oblique muscles of the eye are controlled by a cranial nerve known as the trochlear nerve. Compression of the trochlear nerve can cause eyelid myokymia. Fatigue and stress are also contributing factors in the causation of eyelid myokymia.
- Focal or segmental myokymia: Neuropathies and a history of radiation therapy are associated with focal or segmental myokymia.
- Generalized myokymia: The cause for generalized myokymia (also known as Isaacs syndrome) is not known. The condition may either be present from birth (technically referred to as congenital) or acquired later in life.
Some of the risk factors associated with myokymia include the following:
- Poisons and toxins
- High caffeine consumption
- Gold therapy
- Medical conditions such as autoimmune disorders, thyrotoxicosis, uremia, and myasthenia gravis.
Treatment of Myokymia
Not all cases of myokymia require treatment. For example, transient myokymia resolves on its own without any treatment. In other cases, the treatment of myokymia is tailored to the underlying cause. Myokymia caused by neuropathy may be treated with immunomodulatory therapy. Generalized myokymia may be treated with carbamazepine and phenytoin drugs. In case of seizures, antiepileptic drugs may be given. Surgery may also be an option in case of eyelid myokymia.