A PET study on the characterization of partially reversible radiogenic lower motor neurone disease.
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.


METHODS
A 31-year-old seminoma patient received postoperative para-aortic and para-iliac telecobalt irradiation with a biologically effective dose of 88 Gy(2) (44 Gy in 2 Gy fractions/day, with an estimated alpha/beta 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 [(18)F]fluorodeoxyglucose (FDG) and [(11)C] 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 [(11)C] 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).
Department of Radiotherapy, Semmelweis University, Budapest, Hungary, and Department of Radiotherapy, National Institute of Oncology, Budapest, Hungary.
O
O
Esik
Z
Z
Lengyel
G
G
Sáfrány
K
K
Vönöczky
P
P
Agoston
J
J
Székely
E
E
Lengyel
T
T
Márián
L
L
Trón
I
I
Bodrogi
D000328:Adult; D003037:Cobalt Radioisotopes / Q000009:adverse effects*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D016472:Motor Neuron Disease / Q000000981:diagnostic imaging / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology*; D011867:Radioisotope Teletherapy / Q000009:adverse effects*; D019275:Radiopharmaceuticals; D020127:Recovery of Function; D018239:Seminoma / Q000628:therapy; D015222:Sodium Channels / Q000378:metabolism; D013736:Testicular Neoplasms / Q000628:therapy; D014055:Tomography, Emission-Computed / Q000379:methods
D003037:Cobalt Radioisotopes; D019275:Radiopharmaceuticals; D015222:Sodium Channels; D019788:Fluorodeoxyglucose F18