Myelopathy in Behcet's Disease: The Bagel Sign

Objective: To describe the clinical and distinctive imaging features of myelopathy associated with Behcet's disease (BD). Methods: We evaluated the records of patients meeting the following criteria: (1) fulfillment of the International Study Group criteria for BD; (2) clinically suggestive of myelopathy; (3) simultaneous spinal cord and brain magnetic resonance images (MRIs) within 1 month of acute worsening of myelopathy; and (4) follow-up duration >= 1 year after initial MRI evaluation. Patients not fulfilling all inclusion criteria and having MRIs with poor quality or missing sequences were excluded. Results: In 11 patients (9 men, 2 women), we studied 14 MRIs during distinct myelopathy episodes and nine follow-up MRIs. Two distinct MRI patterns of spinal cord involvement were described according to T2-weighted (T2W) axial images: (1) Bagel Sign pattern: a central lesion with hypointense core and hyperintense rim with or without contrast enhancement; and (2) Motor Neuron pattern: a symmetric involvement of the anterior horn cells. Bagel Sign was present in 13 of 14 myelopathy episodes whereas Motor Neuron pattern was observed in 1 of 14 MRIs. Of the 13 MRIs with Bagel Sign long myelopathy (n=9), both long and short myelopathy (n=2) and short myelopathy (n=2) was observed. All patterns cleared with some residual lesions after steroid use and immunomodulation with associated clinical recovery in patients. Interpretation: The signal characteristics of the Bagel Sign potentially represent venous engorgement and/or acute blood products within the spinal cord. To our knowledge, Bagel Sign has not been observed in other forms of longitudinal myelopathy outside of BD, including neuromyelitis optica.