Anti-MOG encephalitis mimicking small vessel CNS vasculitis

Abstract

Objective: To report 2 patients with anti-myelin oligodendrocyte glycoprotein (MOG)-associated encephalitis who were initially misdiagnosed with small vessel primary CNS vasculitis.

Methods: Review of symptoms, MRI and neuropathologic features, and response to treatment. MOG antibodies were determined in serum and CSF using a cell-based assay.

Results: Symptoms included fever, headache, and progressive mental status changes and focal neurologic deficits. CSF studies revealed lymphocytic pleocytosis, and both patients had abnormal brain MRIs. Brain biopsy samples showed prominent lymphocytic infiltration of the wall of small vessels; these findings initially suggested small vessel CNS vasculitis, and both patients were treated accordingly. Although 1 patient had a relapsing-remitting course not responsive to cyclophosphamide, the other one (also treated with cyclophosphamide) did not relapse. Retrospective assessment of serum and CSF demonstrated MOG antibodies in both cases, and review of biopsy specimens showed absence of fibrinoid necrosis (a pathologic requirement for small vessel CNS vasculitis).

Conclusions: Anti-MOG-associated encephalitis can be mistaken for small vessel CNS vasculitis. This is important because the diagnosis of anti-MOG-associated encephalitis does not require brain biopsy and can be established with a serologic test.

Figure 1. MRI of 2 patients with anti-MOG encephalitis initially misdiagnosed with small vessel CNS vasculitis

Patient 1: (A) Axial T2 MRI sequence showing no abnormalities at disease onset; (B) bilateral involvement of the basal ganglia 4 weeks after disease onset while steroids were being decreased; (C) left cerebral peduncle abnormality at 6-week follow-up; (D) asymmetric large hazy white matter and basal ganglia lesions at 4 months; (E) residual white matter lesions and enlargement of ventricles due to brain atrophy; and (F) new asymmetric large hazy white matter lesions 30 months after disease onset when steroids were discontinued. Patient 2: (G and H) Axial FLAIR sequences showing gyriform hyperintensities with edema similar to abnormalities previously reported in cases of anti–MOG-associated cortical encephalitis.

Figure 2. Brain biopsy of 2 patients with anti-MOG encephalitis initially misdiagnosed with small vessel CNS vasculitis

In patient 1, biopsy of the right temporal lobe showed small vessel perivascular lymphocytic infiltration (A, hematoxylin-eosin staining; B, magnification of the vessel shown in panel A). Inflammatory infiltrates included T and B lymphocytes (not shown) in association with edema, perivascular demyelination, and reactive gliosis (C and D, luxol fast blue staining). In patient 2, biopsy of the left temporal lobe showed marked perivascular lymphocytic infiltrates involving the vessel wall (E, hematoxylin-eosin staining). The infiltrates were also composed of T lymphocytes (F, CD3 immunostaining), B lymphocytes (G, CD20 immunostaining), and macrophages (H, anti-CD68 immunostaining). Myelin staining did not show clear evidence of demyelination (not shown). No necrosis or fibrin deposition was identified (not shown). Scale bar 200 μm in A and C, 500 μm in E, and 100 μm in B, D, and F–H.