Coexistence of anti-SOX1 and anti-GABAB receptor antibodies with paraneoplastic limbic encephalitis presenting with seizures and memory impairment in small cell lung cancer: A case report

Abstract

Purpose: Paraneoplastic neurological syndromes associated with autoantibodies are rare diseases that cause abnormal manifestations of the nervous system. Early diagnosis of paraneoplastic neurological syndromes paves the way for prompt and efficient therapy.

Case report: we reported a 56-year-old man presenting with seizures and rapidly progressive cognitive impairment diagnosed as paraneoplastic limbic encephalitis (PLE) with anti-SRY-like high-mobility group box-1 (SOX-1) and anti-γ-aminobutyric acid B (GABAB) receptor antibodies and finally confirmed by biopsy as small cell lung cancer (SCLC). At the first admission, brain magnetic resonance imaging (MRI) showed no abnormal signal in bilateral hippocampal regions and no abnormal enhancement of enhanced scan. The serum anti-GABAB receptor antibody was 1:100 and was diagnosed as autoimmune encephalitis (AE). The computed tomography (CT) scans of the chest showed no obvious tumor signs for the first time. Although positron emission tomography-computed tomography (PET-CT) revealed hypermetabolism in the para mid-esophageal, the patient and his family declined to undertake a biopsy. The patient improved after receiving immunoglobulin, antiepileptic therapy, and intravenous methylprednisolone (IVMP) pulse treatment. However, after 4 months, the symptoms reappeared. Brain MRI revealed abnormal signals in the hippocampal regions. Reexamination of the cerebral fluid revealed anti-GABAB receptor and anti-SOX-1 antibodies, which contributed to the diagnosis of PLE. SCLC was found in a para mid-esophageal pathological biopsy. Antiepileptic medications and immunoglobulin were used to treat the patient, and the symptoms were under control.

Conclusion: Our findings increase the awareness that patients with limbic encephalitis with cognitive dysfunction and epileptic seizures should be enhanced to detect latent malignancy. Our case also highlights the importance of anti-SOX1 antibodies in the detection of underlying neoplasm, particularly SCLC. Our findings raise awareness of the cognitive impairment seen by patients with limbic encephalitis.

Keywords: anti-GABAB receptor antibody; anti-SOX1 antibody; autoimmune encephalitis; paraneoplastic limbic encephalitis; small cell lung cancer.

Figure 1

Case progress timeline, EEG, and PET-CT. (A) Case progress timeline and vital treatment records. (B) EEG demonstrated epileptiform discharge. (C) PET-CT suggested that the metabolism of para mid-esophageal was increased. The lesion was about 1.7 cm*0.6 cm, the maximum value of SUV was 4.4, and the lesion was poorly demarcated from the adjacent esophageal wall. EEG, electroencephalogram; PET-CT, positron emission tomography-computed tomography; SUV, standard uptake value.

Figure 2

Images from the MRI after the second admission. (A, B) T1-weighted sequences showed slight hypointensity in the hippocampus (yellow arrow). (C, D) T2-weighted sequences showed hyperintensity in the hippocampus (yellow arrow). (E, F) FLAIR showed hyperintensity in the hippocampus (yellow arrow). magnetic resonance imaging; FLAIR, fluid-attenuated inversion recovery.

Figure 3

Paraesophageal space-occupying lesion visible on chest CT. nodular thickening of the horizontal tube wall of the esophagus from the tracheal carina was 2.7 cm*2.0 cm*4.0 cm (yellow square). (A) CT plain scan. (B) Arterial phase. (C) Venous phase. CT, computed tomography.

Figure 4

Pathological examination and immunohistochemistry. (A) Biopsy of paraesophageal lesion (hematoxylin–eosin staining, magnification ×40). (B) Biopsy of paraesophageal lesion (hematoxylin–eosin staining, magnification ×100). (C) The immunohistochemistry demonstrated positive results for synaptophysin. (D) The immunohistochemistry demonstrated positive results for CD56.