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Myoclonus

Myoclonus is brief, involuntary twitching of a muscle or a group of muscles. It describes a symptom and, generally, is not a diagnosis of a disease. The myoclonic twitches or jerks are usually caused by sudden muscle contractions; they also can result from brief lapses of contraction. Contractions are called positive myoclonus; relaxations are called negative myoclonus. The most common time for people to encounter them is while falling asleep ("sleep starts"), but myoclonic jerks are also a symptom of a number of neurological disorders. Hiccups are also a kind of myoclonic jerk specifically affecting the diaphragm. more...

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Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Most often, myoclonus is one of several symptoms in a wide variety of nervous system disorders such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, and Creutzfeldt-Jakob disease.

Anatomically, myoclonus may originate from lesions of the cortex, subcortex or spinal cord. The presence of myoclonus above the foramen magnum effectively excludes spinal myoclonus, but further localisation relies on further investigation with electromyography (EMG) and electroencephalography (EEG).

Familiar examples of normal myoclonus include hiccups and hypnic jerks that some people experience while drifting off to sleep. Severe cases of pathologic myoclonus can distort movement and severely limit a person's ability to eat, talk, and walk. Myoclonic jerks commonly occur in individuals with epilepsy. The most common types of myoclonus include action, cortical reflex, essential, palatal, progressive myoclonus epilepsy, reticular reflex, sleep, and stimulus-sensitive.

Types

Classifying the many different forms of myoclonus is difficult because the causes, effects, and responses to therapy vary widely. Listed below are the types most commonly described.

Action myoclonus is characterized by muscular jerking triggered or intensified by voluntary movement or even the intention to move. It may be made worse by attempts at precise, coordinated movements. Action myoclonus is the most disabling form of myoclonus and can affect the arms, legs, face, and even the voice. This type of myoclonus often is caused by brain damage that results from a lack of oxygen and blood flow to the brain when breathing or heartbeat is temporarily stopped.
Cortical reflex myoclonus is thought to be a type of epilepsy that originates in the cerebral cortex - the outer layer, or "gray matter," of the brain, responsible for much of the information processing that takes place in the brain. In this type of myoclonus, jerks usually involve only a few muscles in one part of the body, but jerks involving many muscles also may occur. Cortical reflex myoclonus can be intensified when patients attempt to move in a certain way or perceive a particular sensation.
Essential myoclonus occurs in the absence of epilepsy or other apparent abnormalities in the brain or nerves. It can occur randomly in people with no family history, but it also can appear among members of the same family, indicating that it sometimes may be an inherited disorder. Essential myoclonus tends to be stable without increasing in severity over time. Some scientists speculate that some forms of essential myoclonus may be a type of epilepsy with no known cause.
Palatal myoclonus is a regular, rhythmic contraction of one or both sides of the rear of the roof of the mouth, called the soft palate. These contractions may be accompanied by myoclonus in other muscles, including those in the face, tongue, throat, and diaphragm. The contractions are very rapid, occurring as often as 150 times a minute, and may persist during sleep. The condition usually appears in adults and can last indefinitely. People with palatal myoclonus usually regard it as a minor problem, although some occasionally complain of a "clicking" sound in the ear, a noise made as the muscles in the soft palate contract.
Progressive myoclonus epilepsy (PME) is a group of diseases characterized by myoclonus, epileptic seizures, and other serious symptoms such as trouble walking or speaking. These rare disorders often get worse over time and sometimes are fatal. Studies have identified at least three forms of PME. Lafora body disease is inherited as an autosomal recessive disorder, meaning that the disease occurs only when a child inherits two copies of a defective gene, one from each parent. Lafora body disease is characterized by myoclonus, epileptic seizures, and dementia (progressive loss of memory and other intellectual functions). A second group of PME diseases belonging to the class of cerebral storage diseases usually involves myoclonus, visual problems, dementia, and dystonia (sustained muscle contractions that cause twisting movements or abnormal postures). Another group of PME disorders in the class of system degenerations often is accompanied by action myoclonus, seizures, and problems with balance and walking. Many of these PME diseases begin in childhood or adolescence.
Reticular reflex myoclonus is thought to be a type of generalized epilepsy that originates in the brainstem, the part of the brain that connects to the spinal cord and controls vital functions such as breathing and heartbeat. Myoclonic jerks usually affect the whole body, with muscles on both sides of the body affected simultaneously. In some people, myoclonic jerks occur in only a part of the body, such as the legs, with all the muscles in that part being involved in each jerk. Reticular reflex myoclonus can be triggered by either a voluntary movement or an external stimulus.
Stimulus-sensitive myoclonus is triggered by a variety of external events, including noise, movement, and light. Surprise may increase the sensitivity of the patient.
Sleep myoclonus occurs during the initial phases of sleep, especially at the moment of dropping off to sleep. Some forms appear to be stimulus-sensitive. Some persons with sleep myoclonus are rarely troubled by, or need treatment for, the condition. However, myoclonus may be a symptom in more complex and disturbing sleep disorders, such as restless legs syndrome, and may require treatment by a doctor.

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A 50-year-old woman with bilateral vocal cord paralysis and hilar mass
From CHEST, 8/1/05 by Tereza Martinu

A 50-year-old, white woman presented with a 5-month history of failure to thrive and hoarseness. The patient described a progressive decline in her voice, resulting in inability to speak. Concurrently, dysphagia, nausea, and alternating episodes of diarrhea and constipation developed, which resulted in the loss of 35 lb. Vertigo and dizziness became so severe that the patient was eventually unable to stand without falling. She also described headaches, anxiety attacks, an inability to move her eyes, and loss of visual acuity. The patient presented to an outside hospital where otolaryngologic evaluation revealed bilateral vocal cord paralysis. The patient underwent tracheostomy, and a gastrostomy tube was placed for severe weight loss. The patient was transferred to our institution for further evaluation.

During the 4 years prior to her hospitalization, the patient had been seen for multiple somatic and psychiatric complaints, including paresthesias, intermittent vertigo, anxiety, and depression. Based on serologic markers and the presence of mediastinal adenopathy on chest radiography, the patient received a diagnosis of sarcoidosis and/or lupus.

The patient's other medical history was significant for congestive heart failure, hypertension, and gastroesophageal reflux disease. The patient had a 100-pack-year history of tobacco use. She had no occupational exposures or pets. The patient's family history was remarkable for a mother with breast cancer and a grandfather with colon cancer.

On physical examination, the patient's supine BP was 114/74 mm Hg with a pulse of 74 beats/min. Her upright BP was 90/62 mm Hg, with a pulse rate of 85 beats/min. Her temperature was 37.2 Celsius, respiratory rate was 16 breaths/min, and oxygen saturation was 92% on 1 L of oxygen. Generally, the patient appeared cachectic, chronically ill, and older than her stated age. The pupils were accommodating but nearly unreactive to light. There were three to four beats of vertical nystagmus. The patient had marked temporal wasting and tongue fasciculations. There were no oral lesions or cervical, occipital, or supra-clavicular lymphadenopathy. A tracheostomy was in place. The lung fields had poor air exchange, and occasional wheezes were heard. The heart examination revealed regular rate and rhythm without murmurs, rubs, or gallops. The abdomen was remarkable for the presence of a gastrostomy tube and was diffusely tender and slightly distended without hepatomegaly. Neurologic examination was remarkable for global proximal muscle weakness (4/5) and pathologically brisk patellar, biceps, and bracbioradialis reflexes. The patient had mild dysmetria. She had normal tone, normal sensation to pin prick, and down-going toes bilaterally.

Laboratory examination revealed a hemoglobin of 9.9 g/dL (normal range, 12.0 to 15.5 g/dL), mean cell volume of 100 femtoliters (normal, 80 to 98 femtoliters), WBC count of 15.7 x [10.sup.3]/[micro]L (3.2 to 9.8 x 10a/[micro]L), and a platelet count of 552 x [10.sup.3]/[micro]L (normal range, 150 to 450 x [10.sup.3]/[micro]L). Chemistries, electrolytes, and coagulation profiles were all within normal limits. Thyroid-stimulating hormone was 0.21 [micro]IU/mL (normal, 0.34 to 5.66 [micro]IU/mL), and free thyroxine level was 0.57 ng/dL (normal, 0.52 to 1.21 ng/dL). Serum rapid plasma reagin was nonreactive. The erythrocyte sedimentation rate was 22 mm/h (normal, 0 to 15 mm/h), the anti-nuclear antibody titer was positive at 1:2560 dilution (high titer) with speckled and nucleolar patterns, and the anti-DNA antibody was 9 IU/mL (negative defined as < 30 IU/mL). An HIV-1 antibody test result was negative. Analysis of cerebrospinal fluid was completely normal.

ACT of the chest revealed a 2- by 2.3-cm left hilar mass and a small area of honeycombing (Fig 1). MRI of the brain showed nonspecific loci of T2 hyperintensity within the periventricular white matter, predominantly within the right cerebral hemisphere. Electromyography demonstrated typical myopathic motor units at the right deltoid without signs of acute or chronic denervation. Direct laryngoscopy revealed true bilateral vocal cord paralysis. The cords were fixed in the paramedian position with bilateral bowing of the cords and decreased laryngeal elevation (Fig 2).

[FIGURES 1-2 OMITTED]

What additional tests' are needed at this point in order to establish the diagnosis?

Diagnosis: Anti-Hu paraneoplastic sensory neuronopathy

DISCUSSION

Paraneoplastic syndromes occur in 10 to 20% of patients with lung cancer. The most common paraneoplastic syndrome in lung cancer is hypercalcemia, seen most commonly in tumors of squamous cell histology. Of all the histologic forms of lung cancer, small cell lung cancer is associated with the greatest frequency and diversity of paraneoplastic syndromes, including Cushing syndrome, syndrome of inappropriate anti-diuretic hormone secretion, and rare paraneoplastic neurologic syndromes.

Several neurologic syndromes have been described in association with small cell lung cancer, including paraneoplastic encephalomyelitis and sensory neuropathy, paraneoplastic cerebellar degeneration, cancer-associated retinopathy, opsoclonus-myoclonus, and Lambert-Eaton myasthenic syndrome. Nearly all these paraneoplastic syndromes are associated with the presence of atypical antibodies in the sera. Anti-Hu antibodies are associated with paraneoplastic encephalomyelitis, sensory neuronopathy, cerebellar degeneration, and autonomic neuropathy.

Anti-Hu antibodies are anti-neuronal nuclear autoantibodies generated against the Hu antigen found in neurons. Because the developing CNS is sequestered from the immune system by the blood brain barrier, normal adults do not have Anti-Hu antibodies. However, anti-Hu antibodies may be produced in response to small cell lung cancer derived from neural crest cells. Although all small cell lung cancers express Hu antigen, < 20% of all patients with small cell lung cancer have detectable levels of anti-Hu antibodies. Sixty-seven percent of patients with anti-Hu antibodies have other systemic autoantibodies, including anti-nuclear antibody, and thus seem to have a genetic susceptibility to autoimmunity. Although anti-Hu antibodies have been found in ovarian, breast, prostate, and colon cancer, the presence of anti-Hu antibodies is almost always indicative of an underlying small cell lung cancer; the sensitivity and specificity of anti-Hu antibodies for the diagnosis of small cell lung cancer have been found to be 80 to 90%, respectively.

Patients with anti-Hu antibodies do not typically present with symptoms of occult lung cancer; usually they are first affected by neurologic symptoms related to antibody crossreactivity with central and peripheral nerves. Sensory polyneuropathy is the most common neurologic complaint. Other neurologic manifestations include motor and mixed somatic neuropathy, cerebellar symptoms, limbic encephalitis, cranial neuropathy, myopathy, movement disorder, and aphasia. Fasciculations may be present in patients with myopathy. Limbic encephalopathy manifests as seizures, confusion, dementia, depression, anxiety, or cognitive decline. Cerebellar symptoms include gait ataxia, action tremor, and scanning dysarthria. Brainstem involvement presents as oculomotor paresis, sensorineural hearing loss, and tongue fasciculations. Autonomic neuropathy with severe orthostatic hypotension often occurs. Nonneurologic symptoms have also been described. GI dysmotility occurs in > 20% of patients and is the initial complaint in 12% of patients with anti-Hu antibodies.

To our knowledge, true bilateral vocal cord paralysis has not been described in association with a paraneoplastic process. Bilateral vocal cord paralysis is a very rare diagnosis. The most common cause of bilateral vocal cord paralysis in adults is recurrent laryngeal nerve injury as a complication of thyroidectomy. In a review of 240 cases of adult bilateral abductor vocal cord paralysis, the following were found to be the cause of bilateral vocal cord paralysis: 58% of cases occurred following thyroidectomy, 22% had neurologic causes, 6% had malignancy of the neck, 14% had other causes, and 3% of adults were thought to have idiopathic vocal cord paralysis. In addition to this review, > 300 case reports of bilateral vocal cord paralysis have been written. In addition to trauma (blunt, surgical, or postintubation), medical causes of adult-onset bilateral vocal cord paralysis described in the literature include the following: myasthenia gravis; Guillain-Barre syndrome; postinfectious complications of herpes simplex virus, poliomyelitis, diphtheria, and Streptococcus pneumoniae meningitis; thyroiditis; hypokalemia; radiation-induced damage; cisplatin toxicity; vincristine toxicity; organophosphate poisoning; Shy-Drager syndrome; Parkinson disease; diabetes mellitus; systemic lupus erythematosus; polyarteritis nodosa; and stroke. Vocal cord paralysis has also been described in the setting of disruption of both recurrent laryngeal nerves secondary to neck malignancies, and rarely in association with lung cancer.

Patients who present with anti-Hu paraneoplastic disease have a unique clinical course. Their cancer is usually limited to the mediastinum at the time of diagnosis and typically responds better to therapy. In one study of 196 patients with small cell lung cancer treated with standard chemotherapy, 55.6% of patients with anti-Hu antibodies had complete response to therapy, compared to 19.6% without anti-Hu antibodies. Spontaneous regression of small cell lung cancer has also been described. Some have postulated that anti-Hu antibodies are a marker for host defense against small cell lung cancer, thus explaining the limited size and location of this cancer at the time of diagnosis and better response to chemotherapy. Patients with anti-Hu antibodies usually do not die from their small cell lung cancer, but rather from their neurologic disease. Patients often die from autonomic or respiratory complications of their PSN. Although patients have survived for many years with this disease, the median time to death is approximately 7 months. Unfortunately, treatment of small cell lung cancer does not reverse polysensory neuronopathy. Immunotherapy with plasmapheresis and high-dose steroids has been attempted to improve neurologic dysfunction with mixed results. Two series have shown that immunotherapy may prevent further neurologic decline, but this treatment does not reverse pretreatment neurologic dysfunction.

The diagnosis in our patient was made with anti-Hu paraneoplastic sensory neuronopathy based on a positive anti-neuronal nuclear antibody type-1 titer at 1:7,680 (negative is defined as <1:60) and a transbronchial needle biopsy of the left hilar mass revealing small cell lung cancer (Fig 3). The bilateral vocal cord paralysis was thought to be a manifestation of the paraneoplastic process. The patient was treated with carboplatin and etoposide, as well as chest radiation therapy and prophylactic cranial radiation therapy. One and a half years after her initial presentation, she is alive, able to speak, and walks with a walker. As is the case with most patients with Anti-Hu paraneoplastic process, our patient continues to have neurologic problems including severe vertigo and seizures.

[FIGURE 3 OMITTED]

CLINICAL PEARLS

1. Bilateral true vocal cord paralysis may be a manifestation of a paraneoplastic syndrome.

2. Small cell lung cancer associated with anti-Hu antibodies is usually localized to the mediastinum at time of diagnosis and has a less aggressive course than small cell lung cancer without anti-Hu antibodies.

3. Small cell lung cancer with anti-Hu antibodies classically presents with neurologic symptoms rather than pulmonary symptoms.

4. Patients with small cell lung cancer and anti-Hu antibodies' often die of complications of neurologic disease and not of cancer per se.