Progressive myelopathy mimicking subacute combined degeneration after intrathecal chemotherapy

Intrathecal chemotherapy including methotrexate is well documented for neurotoxicity of diverse clinical manifestation. Acute or chronic leukoencephalopathy is the most common type of methotrexate-induced neurotoxicity, and subacute myelopathy is rare. Although its pathogenesis is not fully understood, it is postulated that direct damage of methotrexate to the central nervous system plays a major part and elevated levels of homocysteine and its excitatory amino acid neurotransmitter metabolites (homocysteic acid and cysteine sulfinic acid) could mediate, in part, MTX-associated neurotoxicity. On the while, subacute combined degeneration is a progressive degeneration of the dorsal and lateral columns of the spinal cord, mostly due to vitamin B12 deficiency. The authors report a case of a 15-year-old boy with Burkitt leukemia who developed progressive myelopathy after intrathecal triple therapy (methotrexate, cytarabine, and hydrocortisone) whose clinical and radiologic features were compatible with subacute combined degeneration. The pathogenic mechanism could be explained by biochemical alteration by methotrexate and a possible treatment strategy was discussed.