Autoimmune encephalitis: what the radiologist needs to know

Autoimmune encephalitis is a relatively novel nosological entity characterized by an immune-mediated damage of the central nervous system. While originally described as a paraneoplastic inflammatory phenomenon affecting limbic structures, numerous instances of non-paraneoplastic pathogenesis, as well as extra-limbic involvement, have been characterized. Given the wide spectrum of insidious clinical presentations ranging from cognitive impairment to psychiatric symptoms or seizures, it is crucial to raise awareness about this disease category. In fact, an early diagnosis can be dramatically beneficial for the prognosis both to achieve an early therapeutic intervention and to detect a potential underlying malignancy. In this scenario, the radiologist can be the first to pose the hypothesis of autoimmune encephalitis and refer the patient to a comprehensive diagnostic work-up - including clinical, serological, and neurophysiological assessments.In this article, we illustrate the main radiological characteristics of autoimmune encephalitis and its subtypes, including the typical limbic presentation, the features of extra-limbic involvement, and also peculiar imaging findings. In addition, we review the most relevant alternative diagnoses that should be considered, ranging from other encephalitides to neoplasms, vascular conditions, and post-seizure alterations. Finally, we discuss the most appropriate imaging diagnostic work-up, also proposing a suggested MRI protocol.

Autoimmune encephalitis related to LGI1 antibodies with negative MRI study: Description of two cases

BACKGROUND

Leucine-rich glioma inactivated 1 (LGI1) antibody-related autoimmune encephalitis is easily misdiagnosed clinically because of its complex and diverse clinical manifestations. We present two cases of LGI1 antibody-related encephalitis with negative imaging findings and perform a literature review on this disease entity.

CASE DESCRIPTION

The first case was that of a 60-year-old man who presented with involuntary movement of the paroxysmal right limb. The second case was that of a 66-year-old man who presented with hearing hallucinations, involuntary shaking of the right limb, and progressive cognitive impairment. Both patients in this study showed negative magnetic resonance imaging (MRI) results. Routine cerebrospinal fluid (CSF) and biochemical examinations showed no significant abnormalities, and positive LGI1 antibodies were detected in both the CSF and serum.

CONCLUSION

Based on our experience and the literature review, we recommend that LGI1 antibody-related encephalitis should be considered when faciobrachial dystonic seizures, acute and subacute-onset seizures, low serum sodium (possibly with low CSF chloride), and cognitive-psychiatric disorders are encountered, even in the absence of specific radiographic and altered CSF findings.

18 F-FDG PET and MRI Evaluation of Paraneoplastic Limbic Encephalitis

ABSTRACT

Autoimmune limbic encephalitis (paraneoplastic or nonparaneoplastic) is a rare condition involving autoantibodies against intracellular or cell-surface proteins of neurons. Patients typically present with acute and progressive neuropsychiatric symptoms. Although the criterion standard for diagnosis remains detection of autoantibodies in cerebrospinal fluid, there are characteristic imaging features that can aid in diagnosis, notably abnormalities in the bilateral medial temporal lobes on imaging, particularly with nuclear imaging. Here, we present 18 F-FDG PET findings of paraneoplastic limbic encephalitis in a 65-year-old man.

Translational imaging of TSPO reveals pronounced innate inflammation in human and murine CD8 T cell-mediated limbic encephalitis

Autoimmune limbic encephalitis (ALE) presents with new-onset mesial temporal lobe seizures, progressive memory disturbance, and other behavioral and cognitive changes. CD8 T cells are considered to play a key role in those cases where autoantibodies (ABs) target intracellular antigens or no ABs were found. Assessment of such patients presents a clinical challenge, and novel noninvasive imaging biomarkers are urgently needed. Here, we demonstrate that visualization of the translocator protein (TSPO) with [18F]DPA-714-PET-MRI reveals pronounced microglia activation and reactive gliosis in the hippocampus and amygdala of patients suspected with CD8 T cell ALE, which correlates with FLAIR-MRI and EEG alterations. Back-translation into a preclinical mouse model of neuronal antigen-specific CD8 T cell-mediated ALE allowed us to corroborate our preliminary clinical findings. These translational data underline the potential of [18F]DPA-714-PET-MRI as a clinical molecular imaging method for the direct assessment of innate immunity in CD8 T cell-mediated ALE.

Paraneoplastic Kelch-like protein 11 antibody-associated cerebellar and limbic encephalitis caused by metastatic “burned-out” seminoma – A scar(r)y phenomenon

INTRODUCTION

The diagnosis of paraneoplastic neurologic syndromes is challenging when the primary tumor masquerades as scar tissue (i.e. "burned-out").

METHODS

Case report.

RESULTS

A 45-year-old male patient presented with progressive cerebellar symptoms and hearing loss. Initial screening for malignancy and extensive testing of paraneoplastic and autoimmune neuronal antibodies gave negative results. Repeated whole-body FDG-PET CT revealed a single paraaortic lymphadenopathy, metastasis of a regressed testicular seminoma. Anti-Kelch-like protein-11 (KLHL11) encephalitis was finally diagnosed.

CONCLUSION

Our case highlights the importance of continued efforts to find an often burned-out testicular cancer in patients with a highly unique clinical presentation of KLHL11 encephalitis.

18FDG PET/CT Tumoral and Neurologic Therapeutic Response in a Case of Anti-GABABR Paraneoplastic Limbic Encephalitis

ABSTRACT

A 70-year-old man with a history of small cell lung carcinoma 2 years earlier was addressed for the suspicion of a paraneoplastic limbic encephalitis. Brain 18FDG PET/CT revealed a bilateral amygdalian and hippocampal hypermetabolism, confirming a limbic encephalitis, and concurrent whole-body 18FDG PET/CT showed a small cell lung carcinoma plurifocal metastatic recurrence, consistent with a paraneoplastic limbic encephalitis. 18FDG PET/CT follow-up under chemotherapy revealed an almost complete normalization of brain metabolism and a partial metabolic response of the metastatic recurrence, consistent with the good clinical neurological evolution of the patient. This case highlights the clinical-metabolic imaging correlation in paraneoplastic limbic encephalitis.

Clinical features of nine cases of leucine-rich glioma inactivated 1 protein antibody-associated encephalitis

To investigate clinical features of leucine-rich glioma inactivated 1 protein (LGI1) antibody-associated autoimmune encephalitis (AE). The clinical data were collected and analyzed in nine patients with LGI1 AE. All nine patients (100%) presented acute/subacute onset, had seizures, cognitive impairment, mental/behavioral abnormalities, six had sleep disorders and seven showed hyponatremia. Seizures manifested in three types: faciobranchial dystonia seizure (FBDS) (44%), mesial temporal lobe epilepsy (MTLE)-like seizure (66%), and focal to bilateral tonic-clonic seizure (FBTCS) (77%). Six of nine cases (66%) showed abnormalities in brain MRI, among them four showed high T2/flair signal on unilateral/bilateral hippocampus, two showed high T1/T2 signal on unilateral basal ganglia. All nine patients (100%) showed abnormalities in EEG, among them 1 (11%) showed diffuse slow waves, 8 (88%) showed focal slow waves; 6 (66%) revealed interictal epileptic discharges; ictal EEG was recorded in five patients, two were FBDS, three were MTLE-like seizure.LGI1 antibodies in serum and cerebrospinal fluid were both positive. No signs of tumor were found in all patients. Eight of nine patients received immunotherapy and antiepileptic drug (AED) treatment, one only treated with AED without immunotherapy. Eight patients improved significantly with seizure-free after immunotherapy, only one still had FBDS after immunotherapy and AED treatment. In LGI1 AE hippocampus and basal ganglia were two main targets, the corresponding seizure type was MTLE-like seizure and FBDS respectively. Diagnosis depended on detection of LGI1 antibodies in CSF. The incidence of tumor was low. The effect of immunotherapy was good and AEDs should be considered as add-on symptomatic treatment.

Case Report/Case Series: Rare case of anti-LGI1 limbic encephalitis with rapidly progressive dementia, psychiatric symptoms, and frequently seizures: A case report

RATIONALE

Anti leucine-rich glioma inactivated 1 (LGI1) limbic encephalitis (LE) is rare autoimmune encephalitis, characterized by acute or subacute cognitive impairment, faciobrachial dystonic seizures, mental disorders, and refractory hyponatremia. As a type of treatable rapidly progressive dementia with a good prognosis, early, and accurate diagnosis is essential. We present a case of anti-LGI1 LE who was initially misdiagnosed with Alzheimer disease because his clinical manifestations were similar to Alzheimer disease.

PATIENT CONCERNS

A male patient presenting with rapidly progressive dementia, faciobrachial dystonic seizures, psychiatric disturbance, and refractory hyponatremia was admitted. The scores of Mini-Mental State Examination, Montreal Cognitive Assessment, and Neuropsychiatric Inventory were 19/30, 16/30, and 91/144, respectively. Brain magnetic resonance images indicated moderate atrophy of the hippocampus and abnormally hyperintensities in the left medial temporal and hippocampus.

DIAGNOSIS

The patient was diagnosed with anti-LGI1 LE based on the presence of LGI-1 antibodies in the cerebrospinal fluid and serum and clinical manifestations.

INTERVENTIONS

Patient was treated with glucocorticoid against LGI1, antiepileptic drug, cholinesterase inhibitors, and other adjuvant therapy.

OUTCOMES

The patient showed marked improvement on immunotherapy. Clinical symptoms were disappeared and the LGI-1 antibodies in cerebrospinal fluid and serum were both negative at the time of discharge.

CONCLUSIONS

Recognition of the specific symptoms and LGI-1 antibody test will be helpful for the early diagnosis, prompt immunotherapy, and good prognosis. This case raises the awareness that rapidly progressive dementia with frequent seizures could be caused by immunoreactions.

[Paraneoplastic limbic encephalitis complicating pulmonary adenocarcinoma: a case report]

Limbic encephalitis (LE) is a rare disease often of paraneoplastic origin. It is frequently associated with bronchopulmonary cancer. Diagnosis is based on brain magnetic resonance imaging (MRI). We here report the case of a 54-year-old female patient with a history of active smoking, presenting with chronic dry cough. Chest X-ray showed suspicious right lung opacity. Bronchial fibroscopy and bronchial biopsies were not contributory. Thoraco-abdomino-pelvic computed tomography (CT)-scan and brain CT-scan showed a mass in the right upper lobe classified as T4N2M1a. CT-guided lung biopsy confirmed the diagnosis of bronchopulmonary adenocarcinoma. The patient had reported a recent history of memory disturbances associated with depressed mood, anxiety and paroxysmal confusion. Metabolic screening and tests for detecting infection were normal and brain MRI suggested limbic encephalitis. The evolution was characterized by rapid disease progression; the patient died in about ten days.

Paraneoplastic Limbic Encephalitis Secondary to SCLC on 18F-FDG PET/CT

ABSTRACT

A 67-year-old man with rapidly neurologic deterioration and 15 kg weight loss in 2 months was extensively evaluated by several medical specialties and conventional image examinations, with no diagnostic definition. 18F-FDG PET/CT was performed, showing glycolytic hypermetabolism in the hippocampus, cerebral hypometabolism with posterior temporoparietal pattern, multiple cervical and supraclavicular lymph nodes, and mediastinal hypermetabolic and enlarged lymph nodes, suggesting paraneoplastic limbic encephalitis, Alzheimer dementia, and lymphoma. Lymph node biopsy resulted in small cell lung carcinoma. The patient presented rapid clinical deterioration and died.

18F-FDG PET/CT in Anti-Leucine-Rich Glioma-Inactivated 1 Antibody Encephalitis: Typical Pattern and Follow-up

ABSTRACT

We report the case of a 55-year-old man presenting pseudopsychiatric behavior disorders of subacute-onset. MRI showed a FLAIR (fluid-attenuated inversion recovery) hyperintensity in the left hippocampus. The diagnosis of limbic encephalitis was raised, and the patient was referred for an 18F-FDG PET/CT. PET/CT depicted an increased uptake of the left mesiotemporal structures and also an increased uptake of both cerebellum and striatal areas. This pattern was compatible with an anti-leucine-rich glioma-inactivated 1 antibody encephalitis that was later confirmed.

Metabolic Imaging Patterns on 18F-FDG PET in Acute and Subacute LGI1 Autoimmune Limbic Encephalitis

Autoimmune encephalitis is a diverse group of neuropsychiatric disorders, which are difficult to diagnose clinically. The disorder presents acutely or subacutely with alteration of consciousness, cognitive decline, seizures, and abnormal movements. Autoantibodies are directed against intracellular antigens or extracellular domains of cell surface proteins, critical for neuronal excitability. F-FDG PET/CT has been used to diagnose the metabolic derangement in the brain due to various antibodies. Here we describe a case where acute and subacute phase of disease was visualized on serial F-FDG PET/CT.

Use of diffusion-weighted imaging to distinguish seizure-related change from limbic encephalitis

OBJECTIVE

To determine whether diffusion-weighted imaging (DWI) can help differentiate peri-ictal signal abnormality from limbic encephalitis (LE) among patients with medial temporal lobe T2-hyperintensity.

METHODS

We retrospectively identified patients with peri-ictal medial temporal lobe T2-hyperintensity using a Mayo Clinic database, and reviewed their DWI to look for unique diffusion restriction patterns. We then identified patients with medial temporal lobe T2-hyperintensity and LE, and reviewed their DWI to see if these patterns were ever present. Presence of diffusion restriction patterns was confirmed by a blinded neuro-radiologist.

RESULTS

We identified 10 patients without LE who had peri-ictal unilateral medial temporal lobe T2-hyperintensity, ipsilateral to focal seizure onset. Nine of 10 (90%) had at least one of two diffusion restriction patterns potentially unique to seizure activity; four had gyriform hippocampal diffusion restriction ("Pattern 1"), three had diffuse hippocampal diffusion restriction that spared the most medial temporal lobe structures ("Pattern 2"), and two had both diffusion restriction patterns. The median patient age was 62 years (range 2-76 years) and 3/9 (33%) were female. In comparison, among patients with medial temporal lobe T2-hyperintensity and LE, only 5/57 (9%) had one of the diffusion restriction patterns ("Pattern 2") identified (P < 0.0001); all five had seizures reported.

CONCLUSIONS

In patients with medial temporal lobe T2-hyperintensity and one of the diffusion restriction patterns described herein, the signal abnormality may be a peri-ictal phenomenon rather than indicative of LE and should prompt investigation for seizure. Even in patients with LE, these patterns should raise concern for seizure.

Human hippocampal CA3 damage disrupts both recent and remote episodic memories

Neocortical-hippocampal interactions support new episodic (event) memories, but there is conflicting evidence about the dependence of remote episodic memories on the hippocampus. In line with systems consolidation and computational theories of episodic memory, evidence from model organisms suggests that the cornu ammonis 3 (CA3) hippocampal subfield supports recent, but not remote, episodic retrieval. In this study, we demonstrated that recent and remote memories were susceptible to a loss of episodic detail in human participants with focal bilateral damage to CA3. Graph theoretic analyses of 7.0-Tesla resting-state fMRI data revealed that CA3 damage disrupted functional integration across the medial temporal lobe (MTL) subsystem of the default network. The loss of functional integration in MTL subsystem regions was predictive of autobiographical episodic retrieval performance. We conclude that human CA3 is necessary for the retrieval of episodic memories long after their initial acquisition and functional integration of the default network is important for autobiographical episodic memory performance.

Volumetry of Mesiotemporal Structures Reflects Serostatus in Patients with Limbic Encephalitis

BACKGROUND AND PURPOSE

Limbic encephalitis is an autoimmune disease. A variety of autoantibodies have been associated with different subtypes of limbic encephalitis, whereas its MR imaging signature is uniformly characterized by mesiotemporal abnormalities across subtypes. Here, we hypothesized that patients with limbic encephalitis would show subtype-specific mesiotemporal structural correlates, which could be classified by supervised machine learning on an individual level.

MATERIALS AND METHODS

T1WI MPRAGE scans from 46 patients with antibodies against glutamic acid decarboxylase and 34 patients with antibodies against the voltage-gated potassium channel complex (including 10 patients with leucine-rich glioma-inactivated 1 autoantibodies) and 48 healthy controls were retrospectively ascertained. Parcellation of the amygdala, hippocampus, and hippocampal subfields was performed using FreeSurfer. Volumes were extracted and compared between groups using unpaired, 2-tailed t tests. The volumes of hippocampal subfields were analyzed using a multivariate linear model and a binary decision tree classifier.

RESULTS

Temporomesial volume alterations were most pronounced in an early stage and in the affected hemispheric side of patients. Statistical analysis revealed antibody-specific hippocampal fingerprints with a higher volume of CA1 in patients with glutamic acid decarboxylase-associated limbic encephalitis (P = .02), compared with controls, whereas CA1 did not differ from that in controls in patients with voltage-gated potassium channel complex autoantibodies. The classifier could successfully distinguish between patients with autoantibodies against leucine-rich glioma-inactivated 1 and glutamic acid decarboxylase with a specificity of 87% and a sensitivity of 80%.

CONCLUSIONS

Our results suggest stage-, side- and antibody-specific structural correlates of limbic encephalitis; thus, they create a perspective toward an MR imaging-based diagnosis.

Characterizing memory loss in patients with autoimmune limbic encephalitis hippocampal lesions

Since the publication of Scoville and Milner's (1957) seminal paper, the precise functional role played by the hippocampus in support of human memory has been fiercely debated. For instance, the single question of whether the hippocampus plays a time-limited or an indelible role in the recollection of personal memories led to a deep and tenacious schism within the field. Similar polarizations arose between those who debated the precise nature of the role played by the hippocampus in support of semantic relative to episodic memories and in recall/recollection relative to familiarity-based recognition. At the epicenter of these divisions lies conflicting neuropsychological findings. These differences likely arise due to the consistent use of heterogeneous patient populations to adjudicate between these positions. Here we utilized traditional neuropsychological measures in a homogenous patient population with a highly discrete hippocampal lesion (i.e., VGKCC-Ab related autoimmune limbic encephalitis patients). We observed consistent impairment of recent episodic memories, a present but less striking impairment of remote episodic memories, preservation of personal semantic memory, and recall but not recognition memory deficits. We conclude that this increasingly well-characterized patient group may represent an important homogeneous population in which the functional role played by the hippocampus may be more precisely delineated.

The role of 18F-FDG PET/CT in management of paraneoplastic limbic encephalitis combined with small cell lung cancer: A case report

RATIONALE

Limbic encephalitis is one of the most common paraneoplastic neurological disorders (PND). The role of brain Fluorine-18-fluorodeoxyglucose position emission tomography/computed tomography (CT) in paraneoplastic limbic encephalitis (PLE) and of the whole body 18F-FDG PET/CT in this setting, remains still not well defined.

PATIENT CONCERNS

We report a case of a patient with chronic inflammatory rheumatism, psoriasis and Hashimoto thyroiditis and subsequent appearance of static and dynamic ataxia and episodic memory deficit who was diagnosed as PLE combined with small cell lung cancer (SCLC).

DIAGNOSES

The diagnosis of SCLC was made with EBUS-TBNA of a mediastinal lymph node.

INTERVENTIONS

Whole-body 18F-FDG PET/CT was performed for the initial staging of SCLC, in the planning of radiotherapy treatment, to evaluate therapeutic response and in the follow-up. A dedicated brain scan was included to the same PET session. Whole-body contrast enhanced computed tomography (CT) and contrast enhanced whole-brain MRI were also performed.

OUTCOMES

She was administered neoadjuvant chemioterapy with Cisplatin and Etoposide with concomitant radiotherapy treatment. Whole body 18F-FDG PET/CT showed a complete metabolic response already after 3 cycles of chemioterapy. Brain functional study showed a metabolic pattern characterized by the migration of hypermetabolism in the bilateral hippocampal areas during the therapeutic treatment, which correlated with the persistence of clinical symptoms.

LESSONS

In the era of personalized medicine and targeted therapy, this case highlights the importance of the 18F-FDG PET/CT study as an accurate tool to identify PLE and to guide the diagnostic work-up of the underlying tumor. Considering that most of these are 18F-FDG avid tumors and that the 18F-FDG PET/CT scan is often added to the diagnostic work-up when screening patients for malignancy, this functional imaging can play a decisive role.

The role of cognitive rehabilitation in limbic encephalitis: A case report

RATIONALE

Limbic encephalitis is a parenchymal inflammation caused by viral, bacterial, or other microbial and postinfectious agents, which is usually expressed by multifocal neurological signs and cognitive impairment.

PATIENT CONCERNS

A 50-year-old female was admitted in postacute phase, at our rehabilitative Center, to undertake neuro-motor treatment for a period of 4 months.

DIAGNOSES

The patient was affected by limbic encephalitis. Clinical presentation revealed attention, memory and executive dysfunctions, as well as behavioral changes, emotional dysregulation and reduction of self-awareness.

INTERVENTIONS

The patients received an intensive cognitive and motor rehabilitation training.

OUTCOMES

Neuropsychological assessment and magnetic resonance imaging were performed before and after rehabilitative training to evaluate the cognitive and cerebral changes induced by treatment. The patient showed an improvement in cognitive performances and behavioral aspects.

LESSONS

The reducing cognitive deficits, especially memory deficits, could improve quality of life by using available cognitive resources.

[Diagnostic value of single photon emission computed tomography (SPECT) for patients with non-herpetic acute limbic encephalitis]

To evaluate the diagnostic value of SPECT (single photon emission computed tomography) brain blood flow imaging for patients with non-herpetic acute limbic encephalitis (NHALE). A retrospective review of three patients who had clinical symptoms compatible to NHALE and were positive for anti-N-methyl-d-aspartate-type glutamate receptor (GluRε2) antibody. The patients consisted of a 6-year-old female, a 10-year-old female and a 13-year-old male, all of whom had limbic symptoms and were anti-GluRε2 antibody-positive. In all cases, brain MRI failed to detect any abnormality, but SPECT brain blood flow imaging was able to detect blood flow changes. All three cases showed some abnormality in their brain waves, and one of them also developed epilepsy. SPECT brain blood flow imaging may therefore be helpful for diagnosing NHALE which can lead to the development of either epilepsy or cognitive impairment.

Type 1 diabetes and GAD65 limbic encephalitis: a case report of a 10-year-old girl

Limbic encephalitis is a rare neurological disorder that may be difficult to recognize. Clinical features include memory impairment, temporal lobe seizures and affective disturbance. We report the case of a 10-year-old girl with type 1 diabetes mellitus that presented with seizures, depressed mood and memory changes. The diagnosis of glutamic acid decarboxylase 65 (GAD65) mediated limbic encephalitis relied on cerebral magnetic resonance imaging lesions and high serological and cerebrospinal fluid GAD65-antibodies titers. High-dose steroidal therapy was started with clinical improvement. Relapse led to a second high-dose steroid treatment followed by rituximab with remission. A correlation between serum GAD65-antibodies levels and symptoms was found, demonstrating GAD65-antibodies titers may be useful for clinical follow-up and immunotherapy guidance. This report raises awareness of this serious neurological condition that may be associated with type 1 diabetes, underlining the importance of an early diagnosis and prompt treatment for a better prognosis.

Limbic Encephalitis Associated with Sjögren's Syndrome: Report of Three Cases

Sjögren's syndrome (SS) may be complicated by neurological manifestations. We herein report three women (age range 26-60 years old) who all presented with limbic encephalitis (LE) as the predominant clinical feature 3 months to 15 years after the diagnosis of SS. The 26-year-old patient also developed acute motor axonal neuropathy one week after autoimmune encephalitis. All three patients showed contrast-enhanced MRI lesions and inflammatory cerebrospinal fluid findings, while not displaying any anti-neuronal antibodies and showing a remarkable response to immunotherapy. SS is often overlooked when the symptoms are mild. Therefore, in LE cases with no identifiable cause, serological screening for rheumatologic disorders is recommended.

FDG-PET and MRI in potassium channel antibody-associated non-paraneoplastic limbic encephalitis: correlation with clinical course and neuropsychology

OBJECTIVES

We report a patient with potassium channel antibody-associated non-paraneoplastic limbic encephalitis (NPLE) in whom repeated fluorodeoxyglucose-positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) are correlated with epileptic activity and memory performance during the course of disease.

CASE SUMMARY

A 32-year-old woman suffered from prolonged global amnesia after two generalized tonic-clonic seizures due to NPLE. Initially, MRI showed swelling of the left hippocampus. In FDG-PET, however, bitemporomesial hypermetabolism was seen corresponding to frequent bitemporal independent seizure patterns. Also neuropsychological impairments pointed to a bitemporal involvement at this early stage. In parallel with improved control of electrographic seizure patterns, improvement was seen in FDG-PET and in memory performance. During the whole course, MRI showed only left-sided abnormalities, which correlated with a permanent verbal memory impairment.

CONCLUSION

FDG-PET was more sensitive in showing the initial bitemporal involvement and correlated well with EEG findings and neuropsychological impairment in the acute phase of disease. In contrast, structural MRI better reflected persistent neuropsychological deficits.

Serial 18F-fluoro-2-deoxy-D-glucose positron emission tomography and magnetic resonance imaging of paraneoplastic limbic encephalitis

OBJECTIVES

To review and expand the existing literature of magnetic resonance imaging (MRI) and positron emission tomography (PET) of paraneoplastic limbic encephalitis (PLE).

METHODS

We performed serial MRI and 18F-fluoro-2-deoxy-D-glucose (FDG)-PET in a patient with anti-Ma2-positive PLE. In addition, we reviewed the relevant literature by conducting a search in the Medline database.

RESULTS

We found a total of 7 published patient studies of possible or probable PLE containing both MRI and PET data. In 1 of these reports, the diagnosis of PLE can be regarded as proven. The results of the previous studies are controversial. Epileptic activity and inflammation are assumed to be underlying mechanisms of increased FDG uptake. In our study, we found a focal tracer accumulation in the left medial temporal lobe, which increased during the first 9 months of follow-up and corresponded with an increase of serum anti-Ma2 antibody titers. The MRI findings showed a hyperintense signal change in the left medial temporal lobe without contrast enhancement, which remained unchanged over time.

CONCLUSIONS

The results of functional and structural imaging in PLE may differ substantially. Results of FDG-PET can demonstrate focal hypermetabolism over a long time, which may indicate therapeutic potential. A prospective study with more patients will be needed to clarify the relevance of PET as a possible outcome measure in PLE. Future studies should include scalp or semi-invasive electroencephalographic recordings during PET acquisition.

[CT perfusion abnormalities in a case of non-herpetic acute limbic encephalitis]

We report a 42-year-old woman of non-herpetic acute limbic encephalitis (NHALE) whose CT perfusion (CTP) images revealed abnormalities of the limbic system at the early stage. The patient had high fever, convulsion and memory disturbance soon after having caught a common cold, and was admitted to a hospital where she developed progressive disturbance of consciousness. She was then transferred to our hospital 7 days after the initial manifestations. Although enhanced CT images of the brain failed to find any lesion, CTP images revealed a focal increase in the cerebral blood flow and shortening of mean transit time in the bilateral hippocampi and amygdalae. MRI of the subsequent day showed high signal intensity lesions on diffusion, T2-weighted and FLAIR images at the same area. Her consciousness improved by intravenous administration of high-dose methylprednisolone together with other combination therapies. Her CTP images apparently improved by 5 weeks after the onset, but she was left with mild memory disturbance, amenorrhea secondary to hypothalamic failure, hyperosmia, and hypogeusia. In conclusion, CTP is sensitive enough to detect the lesions of the limbic system even in the early stage of NHALE.

Paraneoplastic limbic encephalitis: diagnostic relevance of CSF analysis and total body PET scanning

We report two cases of paraneoplastic limbic encephalitis (PLE) that differed in their clinical patterns, the underlying tumours, and the associated paraneoplastic antibodies. The first patient was a young adult male, with anti-MA-2 antibodies and testicular tumour. The clinical picture was restricted to limbic involvement. The second patient was a 56-year old, female heavy smoker; with seizures and depression, but also vertigo and diplopia. A low level of serum anti-Hu antibodies led to the detection of a small cell lung carcinoma by total body PET-scanning. In both cases, intrathecal synthesis of CSF oligoclonal IgG bands and of the corresponding paraneoplastic antibodies was demonstrated.

[Paraneoplastic limbic encephalitis in small cell lung carcinoma]

We report about a 63-year-old male patient who complained of a recent onset of confusion. A mediastinal mass had been detected in his chest X-ray three days before admission to our clinic. Surprisingly, a CT scan of the brain revealed no signs of cerebral masses or oedema. MRI demonstrated bright hyperintens signals in the medial aspect of both temporal lobes. Biopsy by mediastinoscopy showed small cell lung carcinoma (SCLC). No distant metastases were found by staging procedures. Cerebrospinal fluid and serum contained antineuronal antibodies (anti-Hu). The combination of symptoms, MRI findings and paraneoplastic antibodies established the diagnosis of paraneoplastic limbic encephalitis in a patient with SCLC. Chemotherapy combined with immunosuppression by corticosteroids was started immediately. The primary tumour responded to therapy but improvement of cerebral symptoms was unsatisfactory. Severe memory loss and personality changes remained unchanged while there was a slight improvement in confusion and hallucinations.

Limbic encephalitis investigated by 18FDG-PET and 3D MRI

Two patients with clinically probable or possible limbic encephalitis (LE) are reported, both cases with typical findings in clinical symptoms (severe neuropsychological deficits and complex partial seizures) and in routine magnetic resonance imaging (MRI) (hyperintense mesiotemporal lesions). Underlying malignancy was identified (rectal carcinoma) in one case but could not be detected in the other patient. The 2 patients were investigated by cerebral 18F-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET) and 3-dimensional (3D) MRI, and abnormalities in metabolic activity were mapped using coregistration of spatially normalized PET and MRI. Highly significant focal hypermetabolism in bilateral hippocampal areas was found in both cases. The authors' findings support FDG-PET coregistered to 3D MRI as a potentially valuable additional tool in the imaging diagnostics of LE. Results are discussed with respect to the clinical symptoms and previously reported imaging findings in the disease.