Acute Steroid-Associated Neurological Worsening in Spinal Dural Arteriovenous Fistula with Conus Medullaris Syndrome and “H-sign”

Spinal dural arteriovenous fistula (SDAVF) is an important but frequently overlooked cause of progressive myelopathy because it can mimic inflammatory spinal cord disorders, leading to delayed diagnosis and inappropriate treatment.^{1, 2} We report two cases of corticosteroid-associated neurological deterioration in patients with SDAVF, highlighting the consequences of delayed diagnosis. Written informed consent was obtained from both the patients for publication of their clinical information and radiological images.

A 53-year-old man presented with a 5-month history of gait difficulty, followed by a 1-month history of urinary incontinence and bowel dysfunction. Neurological examination revealed flaccid paraparesis [Medical Research Council (MRC) grade 2/5 on the right and 3/5 on the left], bilateral hypesthesia and hypoalgesia, absent patellar and Achilles reflexes, and bilateral extensor plantar responses. Contrast-enhanced thoracolumbar magnetic resonance imaging (MRI) demonstrated a T2-hyperintense lesion extending from T3 to the conus medullaris with contrast enhancement (Figure 1a, white arrows). Axial T2-weighted images showed hyperintensity involving the anterior and posterior horns of the spinal gray matter, producing the characteristic “H-sign” (Figure 1b, white arrow). Routine laboratory investigations, cerebrospinal fluid (CSF) analysis, and infectious, autoimmune, and paraneoplastic evaluations were unremarkable, except for an elevated CSF protein level of 82 mg/dL. Although the patient did not meet the diagnostic criteria for myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), inflammatory myelopathy was initially suspected because of the conus medullaris involvement and the spinal cord H-sign. Intravenous methylprednisolone (1,000 mg/day) was initiated based on this presumptive diagnosis. Approximately 6 hours after the first dose, the patient’s paraparesis worsened (MRC grade 0/5 on the right and 1/5 on the left). Given the close temporal association, methylprednisolone was discontinued, and plasmapheresis was initiated. Following the first plasma exchange session, lower-extremity muscle strength improved to MRC grade 3/5 on the right and 4/5 on the left. A total of five plasma exchange sessions were completed. In light of the patient’s acute neurological deterioration, a retrospective review of the initial MRI revealed perimedullary flow voids (Figure 1a, red arrows), raising suspicion for SDAVF. Digital subtraction angiography confirmed an SDAVF supplied by the right T6-7 radicular artery, with dilated perimedullary venous drainage extending from T3 to the conus medullaris (Figure 1c, white arrow). The patient subsequently underwent surgical ligation. Two days after surgery, lower-extremity muscle strength improved to MRC grade 4/5 on the right and 5/5 on the left.

Figure 1.

Imaging findings of the two patients. Panels a-c correspond to Case 1. (a) Sagittal T2-weighted magnetic resonance imaging (MRI) shows hyperintensity extending from T3 vertebra to the conus medullaris (white arrows) and serpiginous perimedullary flow voids (red arrows). (b) Axial T2-weighted MRI demonstrates gray matter–predominant signal abnormality resembling the “H-sign” (white arrow). (c) Angiographic image of the T8 intercostal artery demonstrates early venous drainage into tortuous perimedullary veins (red arrow). Panels d, e correspond to Case 2. (d) Sagittal T2-weighted MRI demonstrates longitudinally extensive spinal cord hyperintensity between the T7-L2 vertebral levels (white arrows) and serpiginous perimedullary flow voids (red arrows). (e) Angiographic image obtained at the T10 intercostal artery demonstrates early venous drainage and tortuous perimedullary veins (red arrow).

An 80-year-old man presented with a 2-year history of progressive gait impairment, bilateral lower-extremity paresthesia, and a 1-year history of urinary incontinence. Early in the course of his illness, he was evaluated at another clinic, where thoracolumbar MRI revealed a T2-hyperintense lesion extending from T7 to L2, with spinal cord expansion below T9 involving the conus medullaris (Figure 1d, white arrows). Based on a presumptive diagnosis of inflammatory myelopathy, he was treated with intravenous methylprednisolone. According to the patient’s history, his neurological symptoms worsened following corticosteroid treatment, and he declined further therapy. He subsequently presented to our institution with progressive neurological deficits. Neurological examination revealed flaccid paraparesis (MRC grade 2/5 on the right and 4/5 on the left), bilateral distal hypesthesia and hypoalgesia, and right patellar hyperreflexia. A retrospective review of the referring MRI revealed perimedullary flow voids (Figure 1d, red arrows), raising suspicion for SDAVF. Spinal angiography confirmed an SDAVF at the T10 level with dilated dorsal perimedullary venous drainage and tortuous fistulous vessels (Figure 1e, red arrow). The patient declined surgical treatment and was managed conservatively with rehabilitation.

SDAVF may closely mimic inflammatory myelopathies, particularly MOGAD, because of the presence of longitudinally extensive spinal cord lesions, conus medullaris involvement, and, occasionally, the spinal cord “H-sign,” although this imaging feature is not specific to MOGAD.^{3, 4} Neurological deterioration following corticosteroid administration has been reported in patients with SDAVF. One proposed mechanism is corticosteroid-induced fluid retention, which may exacerbate venous hypertension and spinal cord congestion.^{5, 6} Consistent with previous reports, both patients experienced neurological worsening shortly after corticosteroid treatment. Although neurological improvement was observed after the initiation of plasma exchange in the first patient, its contribution cannot be determined from these observations alone. In both the patients, perimedullary flow voids were present on the initial MRI but were recognized only upon retrospective review, contributing to the delayed diagnosis. These cases highlight that unexpected neurological deterioration following corticosteroid therapy in patients with presumed inflammatory myelopathy should prompt reconsideration of SDAVF and careful reassessment of MRI findings for perimedullary flow voids. Early recognition and timely spinal angiography are essential to avoid delayed diagnosis, inappropriate immunotherapy, and irreversible neurological disability.^{7, 8}