Motor nervous pathway function is impaired after treatment of childhood acute lymphoblastic leukemia: A study with motor evoked potentials

Background The objective was to evaluate whether motor nervous pathways are affected when patients are treated for childhood acute lymphoblastic leukemia (ALL). Procedure Thirty‐two children with ALL were studied at the end of treatment by means of motor evoked potentials (MEPs) elicited by magnetic stimulation (MS) transcranially and peripherally and underwent a detailed neurological examination. Thirty‐two healthy children matched with them for age, sex, and height served as a control group. Results The latencies of the MEPs were significantly prolonged along the entire motor nervous pathway in the patients with ALL compared with the healthy controls, indicating demyelination in the thick motor fibres. The MEP amplitudes of the distal extremities elicited by stimulation at the brachial plexus and LV spinal level were significantly lowered in the patients treated for ALL, also indicating anatomical or functional loss of descending motor fibres and/or muscle fibres. The MEP amplitudes elicited by cortical MS showed wider variation and no clear abnormalities were found. Neurological signs and symptoms were common after treatment: 41% of the patients had depressed deep tendon reflexes, 31% had fine motor difficulties and 63% gross motor difficulties, and 34% had dysdiadochokinesia. The conduction delay within the peripheral nerve was related to the post‐therapeutic interval after administration of vincristine and the lesions within the CNS to the number of injections of intrathecal methotrexate. Conclusions The present results show adverse effects of the ALL treatment on the entire motor nervous pathways. In our experience, the measurement of MEPs by MS provides an objective, painless, and practical tool for assessing the treatment‐related neurotoxicity in both the CNS and the peripheral nerves. These disturbances in the motor nervous pathways at the end of treatment raise the question of the long‐term effects of ALL treatment on the motor nerve tracts, and have led us to employ MEPs to study these effects in long‐term survivors of ALL. Med. Pediatr. Oncol. 36:345–351, 2001. © 2001 Wiley‐Liss, Inc.