Propriospinal myoclonus (PSM) is an uncommon neurological movement disorder involving involuntary, sudden muscle contractions that originate in the spinal cord. Its name comes from the propriospinal pathways—nerve cell networks extending through the spinal cord that help coordinate movement. In PSM, these pathways are responsible for transmitting the abnormal signals that cause the muscle jerks. A defining feature is the way the contractions travel from a single point in the spinal cord, often the mid-back, spreading both up toward the neck and down toward the legs.
Identifying the Symptoms
The primary symptom of PSM is the occurrence of abrupt, brief, shock-like muscle jerks. These movements most frequently involve the axial muscles of the trunk, abdomen, neck, and hips. This involvement often causes the body to flex forward suddenly, sometimes with enough force to cause a person to lurch or fall if unsupported. The experience is often described as an internal “startle” that happens without an external cause.
A key characteristic is the observable spread, or “march,” of the muscle contraction. The movement begins at a specific level of the spinal cord and travels up and down the spine, recruiting adjacent muscles along the way. The jerks can occur as single events or in repetitive bursts.
These symptoms are often provoked by specific triggers. Unexpected sensory stimuli, such as a sudden noise or a light touch, can initiate a jerk, as can anxiety, stress, or the intention to move. Many individuals find their symptoms worsen when lying down, particularly during the transition to sleep. While these can resemble harmless “sleep starts,” PSM jerks are identified by their consistent origin point and slow spread through the trunk muscles.
Origins and Causes
The causes of propriospinal myoclonus are varied and fall into three main categories. In many cases, a precise cause cannot be identified after extensive medical investigation. When no underlying structural or metabolic disorder is found, a diagnosis of idiopathic PSM is made.
In other instances, PSM is symptomatic of another medical issue affecting the spinal cord. This is known as secondary PSM, where the myoclonus is a direct consequence of damage or irritation to spinal nerve pathways. Conditions responsible for secondary PSM include:
- Structural lesions like tumors or cysts (syringomyelia)
- Physical trauma to the spinal cord
- Inflammatory conditions like myelitis
- Demyelinating diseases such as multiple sclerosis
A third origin is psychogenic PSM, where symptoms are linked to psychological factors rather than a structural spinal problem. It is important to note that these are real, involuntary movements not consciously produced by the patient. This form is often associated with underlying stress, trauma, or other psychiatric conditions and may account for a significant portion of cases previously considered idiopathic.
The Diagnostic Process
Confirming a diagnosis of propriospinal myoclonus involves a careful process to rule out other conditions. The evaluation begins with a clinical assessment, where a neurologist takes a detailed medical history and observes the movements. The patient’s description of the jerks, their triggers, and the pattern of muscle involvement provides important initial clues.
The most important diagnostic tool is electromyography (EMG), which measures the electrical activity within muscles. Electrodes placed on the skin over muscles of the trunk, neck, and limbs record their activity during a myoclonic jerk. In PSM, the EMG reveals a distinct pattern showing muscle activation beginning in a single thoracic spinal segment and then spreading slowly up and down the body.
This slow propagation speed of about 5 to 16 meters per second is a key feature of PSM. It is consistent with signal transmission through the propriospinal nerve pathways and helps differentiate PSM from faster types of myoclonus, such as cortical myoclonus. To complete the diagnosis, an MRI of the spine is often used to search for underlying secondary causes like a tumor or inflammation.
Management and Treatment Approaches
The strategy for managing propriospinal myoclonus is tailored to the underlying cause. If PSM is secondary to another condition like a spinal cord lesion, treatment focuses on that root cause. For example, surgery may be an option to remove a tumor, or medication could be used to manage an inflammatory condition like myelitis.
For idiopathic PSM, treatment is aimed at managing the symptoms with medication. Pharmacological therapy is used to reduce the frequency and intensity of the muscle jerks. Clonazepam, a type of tranquilizer, is often a first-line therapy that works by enhancing the effects of a neurotransmitter that calms nerve activity. Anticonvulsant medications, such as levetiracetam, are also frequently prescribed to modulate nerve signals.
When PSM is determined to be psychogenic, the treatment approach involves a combination of therapies. While medications like clonazepam may still be used to help control the physical symptoms, psychological treatments are also introduced. Cognitive-behavioral therapy (CBT) is particularly helpful, as it assists patients in developing coping strategies for the stressors that may contribute to their symptoms. Other forms of psychotherapy may also be recommended.