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المستخلص
Autoimmune focal encephalitis is a group of diseases. These include Rasmussen encephalitis (RE), Hashimoto encephalopathy, and paraneoplastic and nonparaneoplastic limbic encephalitis.
Limbic encephalitis includes the rapid development of irritability, depression, sleep disturbances, seizures, hallucinations, and short-term memory loss. After excluding a viral etiology, a problem that the physician confronts when initially examining a patient with suspected limbic encephalitis is to determine if the disorder is paraneoplastic or not. This difficulty stems from the fact that in 60% to 70% of paraneoplastic cases, the neurologic disorder precedes the detection of the tumor and conversely, a similar clinical picture, CSF, and MRI findings also occur without cancer association.
These studies suggested 2 broad categories of autoimmune limbic encephalitis: (1) one associated with antibodies to intracellular neuronal antigens, which include among others all previously known paraneoplastic antigens, and (2) one associated with antibodies to cell membrane antigens, including the VGKC, NMDAR, and others that remain to be characterized.
The main intracellular autoantigens related to immunemediated limbic encephalitis are Hu, Ma2, and less frequently CV2/CRMP5, and amphiphysin.
The following investigations may aid the diagnosis: analysis of cerebrospinal fluid (CSF), electroencephalography, fluorodeoxyglucose positron emission tomography and neuronal antibodies in the serum and CSF. MRI shows high intensity signals in the medial temporal lobes and cerebrospinal fluid analysis shows some lymphocytes and oligoclonal bands. There is also serum antibodies to one of the paraneoplastic antigens.
Patients suspected of having autoimmune limbic encephalitis should be considered for immunotherapy (corticosteroids, intravenous immunoglobulin or plasma exchange). Treatment should start even in the absence of antibody testing because patients with limbic encephalitis- can deteriorate rapidly, with status epilepticus, hyponatraemia or hypoventilation that may result in death. Also, some patients with limbic encephalitis of unclear aetiology or without antibodies may show dramatic response to corticosteroids.
Rasmussen’s encephalitis (RE) is another form of autoimmune focal encephalitis it is a rare inflammatory brain disease mainly affecting children and characterised by intractable epilepsy involving a single hemisphere that undergoes progressive atrophy RE is characterized by refractory focal seizures, often associated with epilepsia partialis continua and progressive unilateral motor defect .
Rasmussen’s encephalitis is characterized by diffuse, unilateral cerebral hypometabolism on FDG PET images, with corresponding regions of cerebral atrophy on MR images. Although MR imaging data alone are sufficient to suggest a diagnosis of Rasmussen’s encephalitis in many cases, correlation with FDG PET data increases diagnostic confidence and allows the unequivocal identification of the affected cerebral hemisphere in patients whose MR imaging findings are subtle or distributed bilaterally.
Pathogenic concepts have considered autoimmune antibodies that might contribute to the initiating or perpetuating events in the central nervous system.
Treatment of RE pursues two goals: alleviation of the seizure disorder and cessation of the progressive neurological deficit. Epilepsy surgery has played a major role in seizure treatment of RE since the 1950s. It remains the only ‘cure’ of the disease progression, but not without neurological deficit. There is a controversy as to whether HE should be proposed early in the disease course or only when the neurological deficits, which inevitably induced by the operation. Immunotherapy can used in following regimens (i) corticosteroids; (ii) intravenous immunoglobulins (IVIG); (iii) corticosteroids plus IVIG ; (iv) plasmapheresis (PEX) or protein A IgG immuno-adsorption (PAI) ; and (v) tacrolimus.
Hashimoto’s encephalopathy (HE) is a controversial neurological disorder that comprises a heterogenous group of neurological symptoms that manifest in patients with high titers of antithyroid antibodies. Clinical manifestations of HE may include encephalopathic features such as seizures, behavioral and psychiatric manifestations, movement disorders, and coma. Although it has been linked to cases of Hashimoto’s thyroiditis or thyroid dysfunction, the most common immunological feature of HE is the presence of high titers of antithyroglobulin or anti-TPO (antimicrosomal) antibodies.
At present, it is unclear whether antithyroid antibodies represent an immune epiphenomenon in a subset of patients with encephalopathic processes or they are really associated with pathogenic mechanisms of the disorder. The significance of classifying encephalopathies under the term HE will be determined in the future once the relevance of the role of antithyroid antibodies is demonstrated or dismissed by more detailed experimental and immunopathological studies. The responsiveness of HE to steroids or other therapies such as plasmapheresis supports the hypothesis that this is a disorder that involves immune pathogenic mechanisms. Further controlled studies of the use of steroids, plasmapheresis, or immunosuppressant medications are needed in the future to prove the concept of the pathogenic role of antithyroid antibodies in HE.