Imaging description

Subacute combined degeneration (SCD) is characterized by dysesthesia, disturbance of position sense, and spastic paraparesis or tetraparesis that occurs as a result of demyelination of the white matter tracts in the dorsal and lateral columns of the cervical and upper thoracic cord secondary to vitamin B12 deficiency. MRI shows symmetrical T2 hyperintensity in the posterior and lateral columns of the cord that usually extends in a continuous fashion throughout the cervical cord and sometimes the upper thoracic cord (Fig. 103.1) [1]. Involvement of anterior columns and enhancement on post-contrast sequences are rare. DWI shows restricted diffusion in the same distribution. MRI may be completely normal in some cases, however. Nitrous oxide inhalation, either as an anesthetic agent or as a recreational drug, can act on the vitamin B12 metabolism and result in the same clinical presentation and MRI findings [2]. N2O-provoked SCD may occur in patients who have normal levels of vitamin B12. Copper deficiency is another less common reason for SCD [3].

Importance

Early diagnosis is essential to prevent significant cord damage. After vitamin B12 supplementation, patients show clinical and radiologic improvement. Early initiation of treatment is more likely to result in complete recovery.