Experimental study on subacute neurotoxicity of methotrexate in cats

An experimental study on the pathogenesis of methotrexate (MTX)-related neurotoxicity including disseminated necrotizing leukoencephalopathy (DNL) was conducted in cats. MTX was administered to the cerebrospinal fluid (CSF) of adult cats using either an intracisternal intermittent instillation (ICI) model or an intraventricular continuous instillation (IVC) model. Furthermore, the synergistic effects of CSF-flow disturbance with kaolin-induced hydrocephalus, and 60Co irradiation were morphologically examined in these models. None of the animals from either the ICI and IVC groups showed DNL, but all animals showed segmental axonal degeneration, suggesting that MTX had a direct toxic effect on the axon. In the ICI groups, no apparent synergistic effect of CSF-flow disturbance and radiation was noted on this axonal change. In the IVC groups, CSF-flow disturbance augmented the degree of the axonal injury. Axonal degeneration and fibrin exudation in the walls of small blood vessels occurred in one animal of the IVC groups with CSF-flow disturbance, suggesting that a toxic effect of MTX on blood vessels is another mechanism of MTX-induced neurotoxicity.