¹Department of Radiotherapy, Semmelweis University, Budapest, Hungary

²Department of Radiotherapy, National Institute of Oncology, Budapest, Hungary

³Outpatient Department of Neurology, National Institute of Oncology, Budapest, Hungary

⁴Medical Oncology Department 'C', National Institute of Oncology, Budapest, Hungary

⁵PET Centre, University of Debrecen, Debrecen, Hungary

⁶Department of Molecular and Tumor Biology, National Institute of Radiobiology and Radiation Hygiene, Budapest, Hungary

Correspondence to: O Ésik, Department of Radiotherapy, Semmelweis University, H-1122 Budapest XII, Ráth György u 7-9, Hungary

Objective: To investigate the pathomechanism of the rare radiogenic lower motor neurone disease (LMND) on the basis of a case history involving a partial functional recovery.

Patient: A 31-year-old seminoma patient received postoperative para-aortic and para-iliac telecobalt irradiation with a biologically effective dose of 88 Gy₂ (44 Gy in 2 Gy fractions/day, with an estimated / of 2 Gy) delivered to the spinal cord following a single cycle of chemotherapy. LMND developed 4 months after the completion of radiotherapy. The patient exhibited flaccid paraparesis of the lower extremities (without sensory or vegetative signs), followed by a worsening after further chemotherapy, due to pulmonary metastatization. A gradual spontaneous functional improvement commenced and led several years later to a stabilized state involving moderately severe symptoms.

Methods: In the 15th year of the clinical course, magnetic resonance imaging (MRI) and positron emission tomography (PET) with [¹⁸F]fluorodeoxyglucose (FDG) and [¹¹C]methionine were conducted. Four lines of experiments (clonogenic assay using fibroblasts isolated from a skin biopsy sample of the patient, comet assay, micronucleus assay, and the testing of chromosome aberrations after in vitro irradiation of peripheral blood samples) were performed in a search for an increased individual radiosensitivity.

Results: MRI investigations failed to reveal any pathological change. PET demonstrated an increased FDG accumulation, but a negligible [¹¹C]methionine uptake in the irradiated spinal cord segments. The radiobiological investigations did not indicate any sign of an increased individual radiosensitivity.

Conclusions: We suggest that the observed partial functional recovery and stabilization of the symptoms of radiogenic LMND may be explained by the higher than normal density of sodium channels expressed along the demyelinated axons of the restored conduction. The increased energy demands of this type of conduction are proved by a higher metabolic rate (increased FDG uptake) of the irradiated spinal cord segments without a substantial regenerative process (lack of detectable protein synthesis).

Spinal Cord (2002) 40, 468-473. doi:10.1038/sj.sc.3101316

lower motor neurone disease; irradiation; chemotherapy; functional recovery of conduction; positron emission tomography; sodium channels