Tremor

INDEX

Myorhythmia has been recently defined as a repetitive, rhythmic, often jerky, movement of slow (1–4 Hz) frequency, typically affecting the cranial and limb muscles, often accompanied by palatal tremor and nystagmus.

Lesions frequently involve components of the Guillain-Mollaret triangle, including the dentate nucleus, superior cerebellar peduncle, red nucleus, and inferior olive.

As with palatal tremor, there is frequently a delay between the lesion and the onset of movement.

ORIGIN

Brainstem vascular disease and cerebellar degeneration due to chronic alcoholism or nutritional deficiency.

Other causes include:

Whipple’s disease

NMDA receptor encephalitis

SREAT

Encephalitis with celiac disease

Paraneoplastic

CLASSIFICATION

The term ‘extremity myorhythmia’ has been used when the limbs are predominantly affected; Ocular myorhythmia describes involvement of the eyes. 

CLINICAL FEATURES

Asynchronous and intermittent tremor is seen, predominantly at rest, but are also seen during action or posture, with a frequency between 2 and 3 Hz.  Movements are either pseudorhythmic or nonrhythmic, and frequency and amplitude are variable in the majority. In many cases, the clinical picture is difficult to classify due to its complex and irregular nature, but generally resemble dystonic movements or Holmes’ tremor. When more than one body part is involved the movements may be mutually synchronous, suggesting a common pacemaker.

Oculomasticatory myorhythmia (OMM) may be accompanied by 1 to 3 Hz convergent-divergent pendular or vertical nystagmus, rhythmic eye opening and closing, tongue protrusion or retraction, bruxism, and synchronous rhythmical contractions of the facial and masticatory muscles.

 

OMM is a rare neurological sign of Whipple’s disease (WD). In addition, many patients with WD have vertical ophthalmoparesis. Limb myorhythmia may accompany craniocervical myorhythmia in WD.  Neurological manifestations are common in WD, with cognitive impairment being the most common, noted in 71% of patients, followed by supranuclear ophthalmoplegia (51%) and altered level of consciousness (50%).

Cerebrovascular disease, particularly of the brainstem and thalamus, is the commonest cause of myorhythmia. Commonly limb movements are seen, moving synchronously with the jaw or palate.

AGE OF ONSET

Peak onset of 50–59 years of age.

DISTRIBUTION

Myorhythmia involved primarily the limbs, but also the face, jaw, head and tongue without palatal involvement.

DIFFERENTIAL DIAGNOSIS

Holmes’ tremor.

Both Holmes’ tremor and myorhythmia are characterised by a tremor which tends to be less rhythmic than typical tremor, and also by activity both at rest and during action. However, neither palatal myoclonus nor nystagmus are typical features of Holmes’ tremor. Holmes’ tremor typically has higher amplitude and does not involve cranial muscles.

Epilepsia partialis continua:

This may present with a slower and more rhythmical tremor-like movement which may resemble myorhythmia. However, the EMG burst duration is usually shorter (25-75 msec), and the presence of focal discharges on EEG or EEG jerk-locked discharges, if present, differentiate it from myorhythmia.

Parkinson’s Disease:

Myorhythmia has a lower frequency than PD tremor, and when it occurs in the hands, it is usually more irregular and often has a jerky component without the pronation-supination movement typically seen in patients with PD. Myorhythmia may be rarely associated with parkinsonian signs such as rigidity and bradykinesia. Myorhythmia may be distinguished from a parkinsonian tremor by the lack of L-dopa responsiveness, a more irregular and slower frequency, as well as an intermittent nature.

Dystonic tremor:

Dystonic tremor is usually more irregular, and the movement occurs in the setting of dystonia that diminishes or resolves when the patient is allowed to position the limb into the maximum dystonic posture (“null point”).

PSP:

The vertical gaze palsy which is typical of WD may lead to a misdiagnosis of progressive supranuclear palsy.

Palatal myoclonus:

This is characterized by rhythmical movements of the soft palate that are typically produced by contractions of the tensor or levator veli palatine; they may be synchronous with pharyngeal, laryngeal, neck, diaphragm, and other branchial muscles, occurring at a frequency of 2 to 3 Hz, similar to that observed in myorhythmia. PM and other forms of segmental myoclonus likely lie within the spectrum of myorhythmia.

DIAGNOSTIC TESTS

Electromyography (EMG) studies in patients with myorhythmia typically show pseudorhythmic discharges of motor units lasting approximately 200–300 ms with slow interburst rates of 1–4 Hz. Interestingly, the duration of the discharges is longer than myoclonus but certainly shorter than that of classical tremors.

TREATMENT

Symptomatic treatment of myorhythmia is usually ineffective.