Concomitant Crohn's Disease and Anti-Glutamic Acid Decarboxylase (GAD)-Associated Autoimmune Encephalitis: A Case Report.

Crohn's disease is an inflammatory, autoimmune disorder that predominantly affects the intestines but can also affect extraintestinal organs. Certain neurological conditions, such as autoimmune encephalitis, can develop along with this disease. In this case report, we present a case of anti-glutamic acid decarboxylase (GAD) antibody-associated autoimmune encephalitis that occurred shortly after the diagnosis of Crohn's disease and was unrelated to the treatment and nutritional deficiencies. After a significant weight loss (24 kg) and persistent diarrhea, the patient was diagnosed with Crohn's disease by colonoscopy and biopsy. Within two weeks after the diagnosis, he experienced altered consciousness and memory impairment, followed by a rapid deterioration in consciousness and respiratory distress, leading to intubation and admission to the intensive care unit. His brain MRI revealed asymmetrical diffuse cortical diffusion restrictions, hyperintense signals on fluid-attenuated inversion recovery (FLAIR) sequences, and diffuse pachymeningeal contrast enhancement involving both cingulate gyri, bilateral insular cortices, amygdalae, hippocampi, and the right precuneus. Analysis of cerebrospinal fluid (CSF) revealed a slight elevation of CSF proteins, and the patient tested positive for serum anti-GAD antibodies. The patient responded favorably to a seven-day course of intravenous methylprednisolone, five days of intravenous immunoglobulin (IVIG), and oral corticosteroids. Subsequent treatment consisted of monthly IVIG, azathioprine, and vedolizumab, resulting in no neurologic sequelae except mild amnesia. A follow-up MRI at three months showed a nearly complete disappearance of the lesions. This is the first reported case of anti-GAD-associated encephalitis occurring in the presence of Crohn's disease.