RESUMO
The terms autoimmune dementia and autoimmune encephalopathy may be used interchangeably; autoimmune dementia is used here to emphasize its consideration in young-onset dementia, dementia with a subacute onset, and rapidly progressive dementia. Given their potential for reversibility, it is important to distinguish the rare autoimmune dementias from the much more common neurodegenerative dementias. The presence of certain clinical features [e.g. facio-brachial dystonic seizures that accompany anti-leucine-rich-glioma-inactivated-1 (LGI1) encephalitis that can mimic myoclonus] can be a major clue to the diagnosis. When possible, objective assessment of cognition with bedside testing or neuropsychological testing is useful to determine the degree of abnormality and serve as a baseline from which immunotherapy response can be judged. Magnetic resonance imaging (MRI) head and cerebrospinal fluid (CSF) analysis are useful to assess for inflammation that can support an autoimmune etiology. Assessing for neural autoantibody diagnostic biomarkers in serum and CSF in those with suggestive features can help confirm the diagnosis and guide cancer search in paraneoplastic autoimmune dementia. However, broad screening for neural antibodies in elderly patients with an insidious dementia is not recommended. Moreover, there are pitfalls to antibody testing that should be recognized and the high frequency of some antibodies in the general population limit their diagnostic utility [e.g., anti-thyroid peroxidase (TPO) antibodies]. Once the diagnosis is confirmed, both acute and maintenance immunotherapy can be utilized and treatment choice varies depending on the accompanying neural antibody present and the presence or absence of cancer. The target of the neural antibody biomarker may help predict treatment response and prognosis, with antibodies to cell-surface or synaptic antigens more responsive to immunotherapy and yielding a better overall prognosis than those with antibodies to intracellular targets. Neurologists should be aware that autoimmune dementias and encephalopathies are increasingly recognized in novel settings, including post herpes virus encephalitis and following immune-checkpoint inhibitor use.
RESUMO
PURPOSE OF REVIEW: To describe the clinical, laboratory, and MRI features that characterize cognitive decline in the setting of central nervous system (CNS) autoimmunity, and provide an overview of current treatment modalities. RECENT FINDINGS: The field of autoimmune neurology is rapidly expanding due to the increasing number of newly discovered autoantibodies directed against specific CNS targets. The clinical syndromes associated with these autoantibodies are heterogeneous but frequently share common, recognizable clinical, and MRI characteristics. While the detection of certain autoantibodies strongly suggest the presence of an underlying malignancy (onconeural autoantibodies), a large proportion of cases remain idiopathic. Cognitive decline and encephalopathy are common manifestations of CNS autoimmunity, and can mimic neurodegenerative disorders. Recent findings suggest that the frequency of autoimmune encephalitis in the population is higher than previously thought, and potentially rivals that of infectious encephalitis. Moreover, emerging clinical scenarios that may predispose to CNS autoimmunity are increasingly been recognized. These include autoimmune dementia/encephalitis post-herpes simplex virus encephalitis, post-transplant and in association with immune checkpoint inhibitor treatment of cancer. Early recognition of autoimmune cognitive impairment is important given the potential for reversibility and disability prevention with appropriate treatment. Autoimmune cognitive impairment is treatable and may arise in a number of different clinical settings, with important treatment implications. Several clinical and para-clinical clues may help to differentiate these disorders from dementia of other etiologies.