Classification: Movement disorders
Spasmodictorticollis (ST) is a disorder in which the head is involuntarily rotated or tilted in an orthogonal position due to continuous or intermittent spasms of the neck muscles, commonly including head rotation, tilting to the left and right, forward tilt, and backward tilt. The head and neck not only lose their normal posture, but also their mobility is affected. The most common type of dystonia in adults is the limited seizure, which is more accurately called idiopathiccervicaldystonia (ICD). It is also reported in the literature that the prevalence of spastic dystonia is approximately 9 per 100,000 and its incidence is gender and age dependent, usually 1.5-1.9 times higher in women than in men. The peak age of onset is 50-60 years, with 70-90% of patients developing the disease between the ages of 40 and 70.
Pathogenesis of spastic levator neck
The exact pathological mechanism of spastic levator neck is not yet clear and may be related to the following.
1) Genetic factors: Some adults with limited seizures of dystonia are genetically determined. Much progress has been made in genetic studies of generalized dystonia, and there has been a little progress in genetic studies of limited dystonia under its influence. In some family lines, cervical dystonia is seen in about 10% of first and second degree relatives, with evidence of autosomal dominant inheritance with reduced epizootic rates. In one study of three families of patients with spastic dystonia, it was found that the onset of the disease in one family was associated with chromosome 18P. In contrast, the latter two families lacked involvement of the DYT1 locus in the gene. This suggests the existence of genetic abnormalities in the pathogenesis of limited cervical dystonia.
2) Trauma: Trauma has been considered to be the cause of spastic dystonia, and the literature reports that 9%-16% of patients have a history of previous head or neck trauma, usually occurring weeks to months before the onset of the disease.
3) Vestibular abnormalities: Increased or asymmetrical vestibulo-ocular reflex responsiveness has been reported in patients with spastic squint, which cannot be corrected after treatment with botulinum toxin. Vestibular abnormalities are not primary abnormalities, and other types of limited dystonia (e.g., writing spasms, blepharospasm) can also be associated with spastic leptomeningeal neck. Deafness, vertigo and ataxia are not features of spastic squint. Also, many patients do not have abnormal vestibular reflexes and have prolonged spastic strabismus, which may be secondary to vestibular abnormalities. Spastic squint causes prolonged abnormal head posture.
4) Other: short or prolonged cervical vibration stimulation reveals significant differences in head postural changes in patients due to alterations in peripheral proprioceptive stimuli that involve central control of compensatory head and neck torsional mediation and impaired central integration of afferent nerve impulses.
Clinical manifestations of spastic diagonal neck
The disease mostly starts in adults and can develop in both sexes, but the incidence is slightly higher in women than in men. The onset of the disease is slow and progressive, and rarely subsides or resolves on its own. The abnormal movement of the head and neck muscles is uncontrollable, often involving bilateral muscle groups, but the degree of involvement is often asymmetrical, resulting in a twisting motion of the head to one side.
The disease is aggravated by activity or work stress, and the symptoms decrease or disappear during sleep. Symptoms often appear suddenly as a “pulling or dragging of the neck” or as an involuntary rotation or sharp turn of the head. Atypical symptoms may lead to misdiagnosis of “arthritis, cervical radiculopathy, psychiatric disorders, Parkinson’s or TMJ syndrome. The cheek, eyelid (blepharospasm), arm (writing spasm) and trunk are the most commonly affected areas, with certain triggers and inhibitors characteristic of primary dystonia, represented by contact with the jaw, face and head to reduce dystonia.
Spastic dystonia tends to worsen within 3-5 years, and the duration can vary greatly from 1 month to 18 years. And then there is a tendency for the symptoms to stabilize. After stabilization there may be a slight remission process. However, remission is not obvious, is often incomplete or non-persistent, with a remission rate of about 10-20%, and usually occurs within the first year of onset.
In addition, pain is more prevalent in spastic squints, a feature that helps to distinguish other types of localized dystonia and is associated with functional impairment. Pain is present at some point during the course of the disease in 75% of patients and this pain is the main source of dysfunction. Pain is also associated with the degree of sustained spastic rotation and rotation of the head. Dysfunction is also often caused by avoidance of social interaction due to abnormal head and neck posture.
Treatment of spastic squints
Medication: generally used as an adjunct to botulinum toxin, although there is no experimental evidence of a synergistic effect between the two. High doses and high frequency of Botox injections are associated with neutralizing antibodies. So the specific use of drugs may be to prevent this complication. Anticholinergics, benzodiazepines, baclofen (gamma-aminobutyric acid analogue) tegretol (tranylcypromine preparation) and diphenhydramine are effective in a certain percentage of patients. Anticholinergics, benzodiazepines, baclofen are the most commonly used.
Botulinum toxin injections: chemical denervation with the application of botulinum toxin has dramatically changed the prognosis of patients with cervical clubbing. The most important factor in the application of botulinum toxin is the identification of the pain site and the muscles responsible for the abnormal posture, compared to all previous treatments: botulinum toxin leads to an increased rate of symptomatic improvement in a short period of time and the side effects of this drug treatment are less. A good knowledge of the muscular action of the neck is needed.
The sternocleidomastoid, trapezius, cephalicus and scapular raphe muscles are the commonly injected sites. The number of muscles injected, the number of injections per muscle, and the concentration of Botox applied varies for each patient. The effect usually starts 1 week after the injection and does not exceed 8 weeks per course of treatment, and its effect can be maintained for 12 weeks and can be repeated in 3-4 months. The total amount per course is about 200 U (botox). The efficiency of postural improvement is reported to be 71%, and the efficiency of pain relief is 76%.
Difficulty in lowering the throat, neck weakness and local pain at the injection site are the most common side effects. However, tinnitus, dry mouth, flu-like symptoms, drowsiness, dysphonia, and generalized weakness have been reported. Many studies have shown side effects in 20-30% of patients per treatment cycle, and 50% of patients present at some time during treatment. Most of the side effects are based on the dose applied. Studies applying the maximum dose reported side effects in almost 100% of patients. With smaller doses, the incidence of side effects is less than 7%. It is usually recommended to apply an appropriate low-dose regimen of no more than 300u (BOTOX) per course with an interval of no less than 3 months between doses.
There are two types of treatment ineffectiveness: primary non-response, due to insufficient dose of Botox, incorrectly injected muscles, or some other technical factor. Secondary non-response is due to a change in muscle activity patterns or the formation of neutralizing antibodies. This can be identified by the presence or absence of atrophy in the injected muscles.
One study found that a minimum of 5-10% of patients developed neutralizing antibodies, accounting for 33% of non-responders. Every patient who loses response to injection therapy and does not show atrophy of the injected muscle should be determined to have neutralizing antibodies. Too short an interval between treatments and too high a dose are associated with the development of an antibody response. Botulinum toxin type B and F injections may be considered in cases where botulinum toxin type A is not effective.
Surgical treatment: Surgical treatment is required for those patients whose dystonia is persistent, ineffective to a large number of drugs and botulinum toxin injections and with significant sexual dysfunction.
1) Anterior cervical nerve root and paraneoplastic nerve root dissection: Also known as Foester-Dandy surgery. The anterior nerve roots of the upper cervical 1-3 nerves are cut under the microscope, and the paraneoplastic nerve roots are cut in the plane of the vertebral artery. If the postoperative result is unsatisfactory, the paramedian nerve branch on the diseased side can be further excised in the neck. Postoperative improvement was reported in about 70% of patients, but 1/3 of patients lost the ability to rotate the head autonomously; 1/3 of patients had difficulty in swallowing.
2) Stereotactic surgery: If the myospasm extends beyond the cervical segment, or if other therapies are not effective, this surgery can be used to destroy the medial ventral lateral nucleus of the thalamus. Hassler et al. did interruption of the ForelH thalamic tract surgery for the horizontal rotation type; for the rotation or tilt type, the ventral anterior nucleus of the thalamus (VA) and its pallidum and substantia nigra-thalamic afferent fibers were destroyed, with an efficacy of 36% to 73%. However, the surgery can lead to complications such as hemiparesis, aphasia, and ataxia, and is now less commonly used.
(3) Selective cervical muscle and neurectomy: The head posture of different types of spastic squint is the result of the contraction of each associated muscle, rather than the involvement of all the muscles in the neck. Surgical treatment only needs to target these major muscles, and there is no need to cut the bilateral cervical nerve roots and collateral nerve roots to avoid unnecessary complications. It is also proposed that for rotating type of oblique neck, only the ipsilateral head pinch muscle and the contralateral paraspinal nerve can be removed; for posterior supination type of oblique neck, the left and right part of the trapezius muscle, head pinch muscle, head and cervical semispinal muscle can be surgically removed; for forward flexion type of oblique neck, the bilateral paraspinal nerve can be cut; for lateral bending type of oblique neck, the head pinch muscle and scapular raphe muscle on the head bending side can be done, and individual patients with spasm of ipsilateral sternocleidomastoid muscle can also have additional paraspinal neurectomy.
(4) Selective peripheral neurectomy: This method mainly cuts the posterior branch of the cervical nerve root, and the extent of the cut is selected according to the number of spastic muscle groups. The reason is that all posterior cervical muscles are innervated by the posterior branches of cervical 1-7. This surgical method is effective for rotating type of oblique neck.
(5) Paraneoplastic decompression: The foramen magnum and the spinal canal of the upper cervical segment are opened. Under the operating microscope, we can observe whether there are blood vessels around the paraneoplastic nerve roots bilaterally, usually the blood vessels compressing the nerve are vertebral artery, posterior inferior cerebellar artery or posterior spinal cord artery, and then we can cut the dentate ligament there and put Tefleon wool between the nerve and the compressing blood vessels to isolate them. The surgery is effective in the near term, but the long-term results remain to be seen.