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Lesions more than cerebellum in a puerpera of acute cerebellitis: concurrent encephalitis, not a subtype of ADEM

Key Clinical Message We report a puerpera who has acute-onset ataxia with fever, headache, convulsions, and altered mental status. She had a good response to antivirus treatment and low-dose steroid. Acute cerebellitis was the tentative diagnosis. But concurrent encephalitis was proposed with multiple lesions beyond cerebellum.


Introduction
Acute cerebellar ataxia can be a clinical syndrome with diverse underlying etiology, including neoplastic, vascular, autoimmune, genetic, toxic-metabolic, demyelinating, and inflammatory or infectious diseases. The nomenclature of acute cerebellitis (AC) is adopted if primary infection is considered. AC is usually seen in child patients, characterized by acute-onset cerebellar ataxia with high-grade fever, headache, convulsions, and altered mental status. [1] It is further characterized by CSF pleocytosis and/or neuroradiological evidence of inflammation [2]. We describe a puerpera with characteristic clinical features, CSF, and neuroimaging findings of AC. But multiple lesions of peduncle and splenium of the corpus callosum (SCC) suggest the diagnosis of concurrent encephalitis and propose differential diagnosis of ADEM and postpartum vasculopathy.

Case Report
A 29-year-old woman was admitted to our hospital with a fever of up to 38.5°C, body aches, sore throat, and a slight cough for 2 days. Twenty days before the current admission, she delivered a healthy baby at 35.6 weeks of gestation by cesarean section. On physical examination, temperature was 39.8°C, radial pulse 104, respiratory rate 18, and blood pressure 104/68 mmHg. Blood test showed white blood cell count 9.3 9 10 9 /L, with 78.3% neutrophil. She was given oseltamivir and paracetamol. On day 3, after the onset of fever, she developed convulsions and an altered mental state. Neurological examination revealed signs of dysarthria, nystagmus, bilateral extremities, and trunk ataxia, with negative meningeal signs. On day 4, brain MRI showed well-defined lesions of hypointensity in T1weighted and hyperintensity in T2-weighted imaging without enhancement, and hyperintense in diffusion-weight imaging (DWI) with low apparent diffusion coefficient (ADC) value of bilateral middle peduncle and SCC (Figure 1A-H). MRA/MRV was normal. CSF revealed a WBC count of 29 cells/mm 3 . Gram staining of CSF was negative. Antibodies to EB, CMV, and VDRL were negative. EEG showed diffused slow waves and focal spike waves. On day 6, she complained of recurrent thunderclap headache, and blood pressure of 150/90 mmHg was noted. Dexamethasone IV 10 mg Q12H was added with the tentative diagnosis of AC. After 5 days of treatment, she was free of fever, headache, seizures, and confusions, but she could not walk without help and had prominent dysarthria. A follow-up brain MRI revealed increased lesion in middle peduncle with lower intensity in SCC compared with 6 days prior ( Figure 1I-J); hyperintensity of bilateral hemicerebellum was noted in T2-weighted sequences ( Figure 1M-P); no enhancement in these lesions; dilated lateral and third ventricles; and hyperintense periventricular white matter changes ( Figure 2). On day 20, CSF test revealed no significant finding. On day 45, she could walk without help; brain MRI showed complete recovery of SCC lesion and attenuated lesions in cerebellum and middle peduncle.

Discussion
Acute-onset ataxia is not a rare clinical presentation and has diverse etiology more than inflammation/infection defined in AC. On the other hand, acute cerebellar ataxia (ACA) is usually used in the condition when lack of inflammation/infection features such as fever, prominent meningismus, or a significant alteration of mental state. ACA can be a manifestation of neoplastic, vascular, autoimmune, genetic, toxic-metabolic, and demyelinating disorders. It is believed that ACA constitutes about 50% of cases of ADEM following varicella. [3,4].
Considering the combination of acute ataxia with highgrade fever, headache, convulsion, and altered mental state, inflammatory CSF and abnormal neuroimaging findings in cerebellum, AC was the final diagnosis of this clinical complex case. AC typically occurs as a primary infection and usually occurs in early childhood. [1,2] Although pathologic investigation has been restricted to critically ill patients, it has been suggested that direct invasion by an etiologic pathogen is the main mechanism. Considering the flu-like symptoms, CSF findings, and her immunocompetent state, the most likely cause of her acute ataxia was a virus. Viruses that cause cerebellitis include the enterovirus group, human herpes viruses, measles, and mumps. Many of these are considered as being idiopathic in origin, as in this case.
Bilateral diffuse hemispheric abnormalities represent the most common imaging presentations in AC. Neuroimaging in this case was initially against the clinical reasoning. It showed multiple lesions of bilateral peduncle and SCC in acute stage, as well as lesions of the cerebellum cortex in subacute stage. In a study of 11 child patients of rotavirus cerebellitis, three cases have the similar imaging changes as in this case. Acute rotavirus cerebellitis concurrent with encephalitis was proposed with abnormal EEG and clinical features of encephalitis, including headache, convulsions, and altered mental state. [5] This is a reasonable interpretation of such complex clinical features. Transient SCC lesion is a prominent and distinct change in this case. Transient or reversible lesions in SCC have been reported, which are circumscribed and located in the median aspect of the SCC, hyperintense on T2-weighted, and isohypointense on T1-weighted sequences, with no contrast enhancement. On DWI, lesions of bilateral peduncles and SCC are hyperintense with low ADC values, reflecting restricted diffusion due to cytotoxic edema. The common element is the disappearance of imaging abnormalities and clinical improvement with time. The most established and frequent causes of reversible focal lesions of the SCC are viral encephalitis, antiepileptic drug toxicity/withdrawal, and hypoglycemic encephalopathy. [6]. Reversible lesion of SCC was consistent with the infectious disorder and good recovery in this case.
ADEM was one of the tentative diagnoses based on the first brain MRI in our patient. This case's clinical manifestation was consistent with encephalitic type. Multiple lesions seen in the MRI opened the diagnosis to further consideration. ADEM is a postinfection/vaccination disorder in the strict sense, and it is postulated that host MBP became immunogenic. Because any portion of the nervous system may be affected in ADEM, it is not surprising that variable clinical syndromes may occur. The neuroimaging of ADEM usually show multiple lesions involving white matter, on DWI, and the demyelinating lesions are characterized by high ADC value because of free diffusion. In our case, imaging changes including low ADC value, involvement of cortex of cerebellum, and transient SCC lesion revealed the distinct differences between AC and ADEM clearly, even though there were multiple lesions outside of the cerebellum. Clinical features also favored the diagnosis of a primary CNS infection disease, including 2-day prodromal phase, high-grade fever, convulsion, altered mental state, and response to low-dose steroid. As a possibility, concurrent pregnancy-related stroke and postpartum vasculopathy were considered. Isolated infarctions of bilateral peduncle and splenium are rare, but have been reported, including posterior reversible encephalopathy syndrome [7]. This patient's recurrent thunderclap headache and elevated blood pressure are suggestive of postpartum vasculopathy, a reversible cerebral vasoconstriction syndrome (RCVS), which is characterized by reversible segmental arterial vasoconstriction on serial brain imaging especially in posterior circulation. In this case, the inflammatory CSF changes argued RCVS as a common sense, but 36/62 patients revealed abnormal CSF in one study, among which 16 had slightly elevated CSF WBC (mean: 12/mm 3 , range: 5-35). [8] Therefore, the CSF changes could not be a strong evidence to rule out RCVS. But with the second MRI, we found that the recurrent thunderclap headache and elevated BP were probably induced by obstructive hydrocephalus because of swollen hemispheres of cerebellum.

Conclusion
We prefer the diagnosis of AC in this adult case, although with multiple lesions beyond cerebellum. But differential diagnoses, including ADEM and postpartum vasculopathy are proposed because of atypical imaging findings of AC. In this case, lesions of SCC and peduncle even showed up before that in cerebellum. So lesions outside cerebellum in the clinical scenario of ataxia probably predict the subsequent involvement of cerebellum, and as such, appropriate treatments must be given in order to prevent obstructive hydrocephalus and cerebral hernia.