The corticobasal syndrome triggered by central pontine myelinolysis

Development of Parkinsonism in a Patient with Central Pontine Myelinolysis

Osmotic demyelination syndrome (ODS) is caused by damage to the pons myelin sheath and nerve cells. Although the pathophysiological mechanism responsible for the damage is not yet fully understood, it is currently believed that osmotic-type changes (especially if they are massive and too rapid) cause oedema that leads to compression and, subsequently, demyelination of white matter fibres. It generally manifests with acute paraparesis/tetraparesis, dysphagia, dysarthria, diplopia, and loss of consciousness, as well as hallucinations, spasms, and other neurological symptoms related to brainstem damage. In extreme cases, the locked-in syndrome may also appear. Of note, in some cases an association between osmotic demyelinating damage and the onset of movement disorders has been documented and, although the pathophysiology is still unknown, a correlation has been postulated between ODS and movement disorders. Here, we present a patient with ODS who developed parkinsonism, thus supporting the hypothesis of a correlation between these pathological events.

The Spectrum of Movement Disorders in Cases with Osmotic Demyelination Syndrome

Background

Osmotic demyelination syndrome (ODS) can be a central pontine myelinolysis (CPM) and extrapontine myelinolysis (EPM) based on the regions involved even though they share the same disease process, aetiopathogenesis and time course.

Objectives

Present study aims to characterize the clinical, radiological features and the outcome of patients with ODS with movement disorders as the forthcoming manifestation.

Methods

Chart review of patients with ODS with movement disorders. Demographic, clinical and radiological details of the patients were reviewed.

Results

Eleven patients (six females; mean age: 48.3 ± 17.6 years) were included in the study. Parkinsonism alone and parkinsonism with dystonia was noted in four patients each (36.4%) while dystonia alone was noted in the other 3 (27.3%). Five patients (45.5%) had postural tremors. While 5 patients had dystonia early in the course of illness (3-7 days), it was delayed (6-9 months) in the other 2. A triphasic course was noted in two patients. The first phase of hyponatremia induced neurological impairment was followed by a second phase of worsening due to the immediate effect of ODS and a third delayed phase of worsening due to delayed effect of ODS. MRI showed both EPM and CPM in eight patients, EPM alone in two patients and CPM alone in 1 patient. Nine patients had a good outcome with mRS < 3.

Conclusion

Parkinsonism and dystonia are important manifestations of ODS. Triphasic course with a delayed phase of worsening of movement disorders is probably due to the maladaptive neuronal repair. The concept of triphasic ODS is first being described in our series.

[Diagnoses of corticobasal syndrome and corticobasal degeneration]

Experts use the term corticobasal syndrome (CBS) for patients with a clinical diagnosis of corticobasal degeneration (CBD), and reserve CBD for those whose conditions have been diagnosed on the basis of neuropathological analyses. Several studies demonstrated that patients with CBD may also present with progressive supranuclear syndrome (PSPS), aphasia, Alzheimer disease-like dementia or behavioral change, suggesting that CBS is merely one of the presenting phenotypes of CBD. Although previous CBD diagnostic criteria reflected only CBS, the international consortium proposed new diagnostic criteria for CBD in 2013 (Armstrong's criteria). The new criteria include 4 CBD subtypes; CBS, frontal behavioral-spatial syndrome (FBS), nonfluent/agrammatic variant of primary progressive aphasia (naPPA)，and PSPS. These subtypes were combined to create 2 sets of criteria: more specific clinical research criteria for probable CBD (cr-CBD) and broader criteria for possible CBD that are more inclusive but have a higher chance to detect other tau-based pathologies (p-CBD). Two studies have already revealed that the sensitivity and specificity of the criteria were not high. Because therapeutic interventions that target abnormally-phosphorylated tau have started, further refinement of the criteria is needed via biomarker researches with prospective study designs.

Movement disorders and the osmotic demyelination syndrome

With the advent of MRI, osmotic demyelination syndromes (ODS) are increasingly recognised to affect varied sites in the brain in addition to the classical central pontine lesion. Striatal involvement is seen in a large proportion of cases and results in a wide variety of movement disorders. Movement disorders and cognitive problems resulting from ODS affecting the basal ganglia may occur early in the course of the illness, or may present as delayed manifestations after the patient survives the acute phase. Such delayed symptoms may evolve over time, and may even progress despite treatment. Improved survival of patients in the last few decades due to better intensive care has led to an increase in the incidence of such delayed manifestations of ODS. While the outcome of ODS is not as dismal as hitherto believed - with the acute akinetic-rigid syndrome associated with striatal myelinolysis often responding to dopaminergic therapy - the delayed symptoms often prove refractory to medical therapy. This article presents a review of the epidemiology, pathophysiology, clinical features, imaging, and therapy of movement disorders associated with involvement of the basal ganglia in ODS. A comprehensive review of 54 previously published cases of movement disorders due to ODS, and a video recording depicting the spectrum of delayed movement disorders seen after recovery from ODS are also presented.