Clinical diagnosis
Case 97
【Progress】His disorientation was severe. The communication with family members, doctors and nurses was difficult. His medical condition was getting worsened. He received tracheotomy, being under respiratory control. He was given steroid pulse therapy for two weeks. His tracheotomy is going to be closed, expecting improvement of his symptoms.
【Discussion】
Limbic encephalitis is caused by many autoimmune antibodies and categorized into neoplastic and non-neoplastic neoplastic. As neoplastic limbic encephalitis, small cell carcinoma of the lung, germ cell tumors of the testis and ovarian tumors (mostly teratomas) are listed, and Anti-Hu, Anti-Ma2 and Anti-HMDAR are reported to be the causative antibody, in each restrictive tumor (1-3). These tumors are relatively undifferentiated tumor. Limbic system is a primitive neuric system. The common antigen between the undifferentiated tumor and limbic system is considered to exist.
Meanwhile, as non-neoplastic limbic encephalitis, herpes simplex virus infection, systemic lupus erythematosus (SLE) and other non-identified condition are listed. VGKC (voltage-gated potassium channel) antibody is known to be mostly frequent causative autoimmune antibody in non-neoplastic limbic encephalitis (1-3). Besides that, there are a number of antibodies to nerve surface and myelin protein that are becoming to be known (1-3). Our case had no diseases of neoplastic tumor, herpes simplex virus infection and SLE, and specific autoimmune antibody was not found, implying no identification of causative antibody.
Main structures of limbic system include mammillary body (hypothalamus), fornix, para-hippocampus, hippocampus, anterior nucleus of the thalamus, cingulate gyrus and amygdala (4). Amygdalate situates at the lower anterior end of hippocampus and connects to para-hippocampal gyrus and cingulate gyrus via thalamic dorsal-medial nucleus. Limbic encephalitis damages to not only these components and extra-limbic system such as inferior frontal lobe and insula. In our case, MRI with diffusion showed high signal intensity in limbic system and extra-limbic system insula, pulvinar of thalamus and inferior frontal lobe of the left hemisphere.
As imaging modality to visualize limbic encephalitis, MRI is superior to CT. MRI with fluid attenuation inversion recovery (FLAIR) and diffusion weighted image (DWI), and Gd-contrast enhanced MRI are believed to be sensitive and precede MRI with T2WI (5-7). In our case, Gd-contrast MRI was not conducted and MRI with diffusion preceded to MRI with T2 and FLAIR.
Insula is hidden under Sylvian fissure. Some researchers think insula is the fifth lobe. Others think it is a part of temporal lobe or a group with the limbic systems (8). The lid covering Insula compose of temporal, frontal and parietal lobes. Because the function of Insula was previously least known. The function of Insula at present is a target of research frontier. It gets information via thalamus and connects not only to amygdala interactively but also many association cortical areas. Insula anatomically divided into anterior and posterior parts. In short, the anterior part gets information from thalamus and connects to amygdala and the posterior part gets information from thalamus and connect to the variable association cortical area such as somatosensory and viscero-sensory cortex. Insula is involved in a large number of widely different functions: compassion and empathy, perception, self-awareness, motor control, cognitive functioning and interpersonal experience (9, 10). In addition, it is related to drug abuse and addiction (8-10).
Progressive expressive aphasia which is the deterioration of language function to lose the ability to communicate fluently while still being able to comprehend each word. It is found in Pick’s disease, cortico-basal degeneration, frontotemporal dementia and Alzheimer’s disease (10). It is associated with hypometabolism and atrophy of the left anterior insular cortex. In our case with disorder of left limbic system and left insula, disabilities of communication and speaking was found.
【Summary】
We present a seventy six-year-old male suffering from disorders of orientation, cognition, speaking and convulsion. MRI with DWI showed high signal intensity on left limbic system, anterior frontal lobe and insula, implicating diagnosis of limbic encephalitis. We should keep in mind that limbic encephalitis is caused by autoimmune antibody, and MRI with DWI precedes to visualize the lesion limbic encephalitis rather than MRI with T2WI and FLAIR. Further, Insula which is considered to be the fifth lobe gets information from thalamus and connects amygdala and many association cortical areas, implying to be involved in unimaginable diverse functions such as compassion and empathy, perception, self-awareness, motor control, cognitive functioning and interpersonal experience.
【References】
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2018.3.21