Introduction

Parkinsonism is mostly due to Parkinson’s disease, vascular parkinsonism, dementia-parkinsonism or drug-induced parkinsonism. Other than drug-induced causes of secondary parkinsonism account for a small percentage of cases of parkinsonism and can be due to several causes. One of the possibilities is extrapontine myelinolysis (EPM). Myelinolysis results from rapid correction of hyponatremia and is generally located central in the pons, so-called central pontine myelinolysis (CPM) but can also be located outside the pons (EPM). Here, we describe a case of parkinsonism due to EPM without CPM with 4-year clinical and radiological [magnetic resonance imaging (MRI)] follow-up and we review the recent literature on this subject.

Case report

A 63-year-old woman was admitted to the hospital because of nausea, vomiting, difficulty speaking and impairment of coordination of her arms and legs. Laboratory studies showed a severe hyponatremia of 104 mmol/l which resulted in an acute metabolic encephalopathy. This was corrected initially using hypertonic NaCl 1.5% and later using isotonic NaCl 0.9% infusions. After 18 h the sodium concentration raised to 121 mmol/l and 36 h later it was 130 mmol/l. During 1 week of hospitalisation, she experienced an improvement and was discharged from the ward with a slight dysartria. In the past she had been diagnosed with breast carcinoma, diverticulosis and had undergone a cholecystectomy. Furthermore, she suffered from hypertension and was on drugs for this: B-blocking agent and diuretics (triamtereen-epitizide). The use of diuretics in combination with the vomiting was thought to have caused the severe hyponatremia and the drugs were discontinued.

Eight days later she was readmitted to hospital with progressive dysartria, bradykinesia and loss of “strength” of her arms and legs. Within several days she deteriorated to a bed-ridden stage. Two weeks after this deterioration, without a clear diagnoses, she was referred to the neurology department in our hospital.

During neurological examination the patient was alert and well-oriented. MMSE was 28/30, where she lost two points on memory and visuo-construction. She had a masked face and hypo-phonic speech. Examination of the cranial nerves showed no abnormalities, with normal eye movements. Her upper and lower limbs showed, left more than right-sided, rigidity with cogwheeling and bradykinesia. She had difficulty raising from a chair, and when walking her armswing was decreased. The postural reflexes were impaired. No tremor, dystonia or dyskinesias were noted. The remaining neurological examination was without abnormalities.

Blood tests showed no abnormalities. Sodium was 142 mmol/l, potassium 3.5 mmol/l, ceruloplasmin and copper were normal, thyroid function and lactate in blood were normal, as was the chest X-ray. The T2-weighted images of the MRI of the brain showed bilateral and symmetric increased intensities in the nucleus caudatus and the putamen with sparing of the globus pallidus (Fig. 1, top). There was no abnormal signal in the pons (Fig. 1, top). T1-weighted images of both regions were normal.

Fig. 1
figure 1

Top T2-weighted magnetic resonance scan image showing bilateral symmetrical hyperintensities in caudate nucleus and putamen with sparing of the pons; there is also typical sparing of the pallidum. Bottom T2-weighted magnetic resonance scan after 4 years of follow-up showing a normal intensities of caudate nucleus, putamen and pons

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Based on the clinical course, history of hyponatremia with correction and the abnormalities on the MRI-scan the diagnosis EPM without CPM was made. The patient recovered slowly and was discharged home with parkinsonism; dysartria, bradykinesia and rigidity. During follow-up at the outpatient clinic the patient gradually recovered from her parkinsonism. Three years and 9 months after discharge neurological examination showed only a mild masked face, but further neurological examination was unremarkable. MRI at this stage showed no abnormalities on T2-weighted and FLAIR images in the nucleus caudatus and the putamen (Fig. 1, bottom).

Discussion

We describe a case of parkinsonism after correction of hyponatremia with radiological evidence of EPM without CPM with the longest follow-up reported in the literature.

EPM without CPM causing parkinsonism has been reported in Pubmed seven times since 1990 (Table 1) [1–7]. In all reported cases, including our own case, a severe hyponatremia with fast correction was described, similar to our case. In seven of these cases an initial improvement of general symptoms due to the hyponatremia (e.g. confusion, epilepsy) was described after correction of the hyponatremia, with a secondary deterioration after which symptoms of parkinsonism developed. Spontaneous recovery of this second episode occurred in days to weeks. Six out of eight showed good recovery, which does not mean complete recovery, after a variable follow-up time.

Table 1 Cases described in literature from 1990 until now with parkinsonism due to EPM without CPM
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EPM without CPM is described in 22% of cases with myelinolysis [8]. These EPM lesions were most frequently seen in the cerebellum (55%), lateral geniculate body (41%), putamen (34%), thalamus (34%) and cerebral cortex/subcortex (34%) [8]. CPM was first described in 1959 by Adams. [9] In a series of 58 cases of myelinolysis with brain autopsy in 47% of patients myelinolysis was confined to the pons, while in 53% of patients lesions were also located outside of the pons; EPM. In 1976 Tomlinson suggested rapid correction of sodium as an etiological factor for myelinolysis [9]. Myelinolysis, however, not only appears in adult or alcoholic patients with hyponatremia but can also occur with normal or elevated serum sodium levels [10]. Nowadays it is believed that myelinolysis is caused by a dysbalance between brain electrolytes, especially sodium and chloride, and organic brain osmolites, e.g. creatine, taurine, glutamate. With the correction of serum hyponatremia a net shrinkage of the brain will occur. Oligodendroglial cells form a network around large neurons and appear to be vulnerable to physical stress related to shrinkage [10] leading to myelinolysis in the typical predeliction sites for CPM and EPM. This dysbalance hypothesis has led to the recommendation that correction of hyponatremia should not excess 8 mmol/l per day [9].

We conclude that EPM is a rare cause of parkinsonism that occurs after an initial period of recovery after rapid correction of hyponatremia. The prognosis based, also on the long term seems favourable, although the possibility of publication bias can lead to overestimation of this good prognosis.