Anti-CASPR2 myeloencephalitis with active replication of hepatitis B virus in the central nervous system: a case report.

Introduction

Autoimmune encephalitis (AE) involves inflammation of the central nervous system, and its most common forms involve auto-antibodies against the N-methyl-d-aspartate receptor, leucine-rich glioma-inactivated protein 1, or contactin-associated protein-like 2 (CASPR2) [1].

CASPR2 forms part of the voltage-gated potassium channel complex in both the central and peripheral nervous systems [1], so anti-caspr2 disease usually involves extensive damage to both systems, leading to limbic encephalitis, Morvan syndrome, cerebellar syndrome, peripheral nerve hyperexcitability, and autonomic dysfunction [2].

AE can be triggered by neurotropic viruses, and this has been well documented for encephalitis involving auto-antibodies against the N-methyl-d-aspartate receptor [3] Chronic infection with hepatitis B virus (HBV) has been linked to neurological complications such as myelitis and Guillain-Barré syndrome [4, 5], but it has never been clearly linked to AE.

Here we report what appears to be the first case of anti-CASPR2 encephalitis linked to chronic HBV infection.

Case presentation

A 20 year-old Han Chinese woman presented at our hospital because of headache and fever, followed one week later by bilateral lower limb weakness, urinary retention, abnormal delirium, and rapid onset of somnolence. She reported that her body weight had decreased by 7 kg over the preceding three weeks. Physical examination at admission showed gross vertical nystagmus in both eyes, weakened bilateral pharyngeal reflex, poor muscle strength in the upper limbs (grade 2 on the left side, 3 on the right side). Bilateral muscle tone was reduced and tendon reflexes were reduced in both upper limbs and absent in both lower limbs. The patient was positive for meningeal irritation and negative for Babinski’s sign. She was normal in other neurological and physical examinations. 21 days after onset, patient presented with positive Babinski sign, increased tendon reflex and muscle tone.

Magnetic resonance imaging revealed multiple lesions in the hippocampus, bilateral basal ganglia, brainstem, cerebellar hemisphere, as well as cervical and thoracic spinal cord (Fig. 1). Lumbar puncture showed normal cerebrospinal fluid pressure of 250 mmH2O, normal cell count (134 × 106/L) and elevated protein (1.22 g/L; normal range, 0.15–0.45 g/L). A cell-based assay revealed an anti-CASPR2 antibody titer of 1:32 in serum, but no such antibody was detected in cerebrospinal fluid. The patient was negative for auto-antibodies against the N-methyl-d-aspartate receptor, glutamate receptors 1 or 2-aminobutyric acid B receptor, a-amino-3-hydroxy-5-methyl-4-isoxazol-propionic acid (AMPA) receptors, leucine-rich glioma-inactivated protein 1, dipeptidyl-peptidase-like protein 6, Iglon5, myelin oligodendrocyte glycoprotein, glial fibrillary acidic protein, aquaporin 4, myelin basic protein, and flotillins 1 or 2. The patient was also negative for oligoclonal bands. Metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid detected 28 copies of HBV-DNA, and HBV load in serum was 2.91 × 107 IU/ml. Chest computed tomography did not reveal HBV-associated occupancy.

Fig. 1

a–b Magnetic resonance imaging of the patient, showing multiple lesions in the hippocampus, bilateral basal ganglia, brainstem, and cerebellar hemisphere. c T2-weighted magnetic resonance imaging revealing lesions in the thoracic spinal cord. d Cell-based assay of anti-CASPR2 antibodies in serum

Based on these findings, the patient was diagnosed with anti-CASPR2 myeloencephalitis and chronic HBV infection. She was given multiple courses of immunoglobulin therapy and entecavir, and her condition gradually improved by the time of discharge. The patient complained only of mild sleep disorder, which had resolved by follow-up at 4 months after discharge. However, at this time, we tested autoimmune antibody again using cell-based assay, which revealed an anti-CASPR2 antibody titer of 1:100 in serum and 1:10 in cerebrospinal fluid.

Discussion

To our knowledge, this appears to be the first case of anti-caspr2 myeloencephalitis apparently linked to chronic HBV infection. Interestingly, we found that the titer of anti-CASPR2 antibody in serum and cerebrospinal fluid increased despite improvement in the patient’s condition. Previous studies suggested that there was no definite linear relationship between severity of disease and antibody titer [1].

How AE begins remains unclear. Some AE patients present tumors, such as ovarian teratoma in a patient with encephalitis involving antibodies against the N-methyl-d-aspartate receptor [6], and a thymoma in a patient with anti-caspr2 encephalitis [2]. Viral infection also appears capable of triggering AE: cases of encephalitis involving antibodies against the N-methyl-d-aspartate receptor have been linked to infection by herpex simplex virus, H1N1 influenza virus, influenza B virus, and severe acute respiratory syndrome coronavirus 2 [3, 7]. Some patients have been reported to have chronic HBV infection as well as neurological disorders including acute disseminated encephalomyelitis, neuromyelitis optica spectrum disorders, and Guillain-Barré syndrome [4].

When the body begins to generate antibodies against the invading virus, some of those antibodies may recognize auto-antigens on the surface of cells. For example, epitopes on HBV appear to resemble areas on myelin basic protein, such that the body’s anti-HBV antibodies may bind to the myelin sheath on axons, leading to demyelination and inflammation [8]. This model may explain how viral infection can lead to AE. Consistent with this idea, anti-CASPR2 antibodies in patients with AE recognize extracellular epitopes of CASPR2 [1]. Indeed, chronic HBV infection in patients with neurotic myotonia (Isaacs syndrome) can elicit production of auto-antibodies against the voltage-gated potassium channel complex in which CASPR2 functions [9]. Therefore we speculate that HBV infection of the nervous system may trigger production of auto-antibodies against CASPR2, inducing AE.

Conclusion

HBV may trigger anti-CASPR2 myeloencephalitis. Our case suggests that patients with chronic infections such as HBV who are suspected of having encephalitis should be screened by mNGS and assay of AE-related antibodies in the cerebrospinal fluid.