Postradiation Lower Motor Neuron Syndrome: A Case Report and Brief Literature Review

Abstract

Radiation-induced damage to the spinal cord and the closer nervous structures may either result in a transient myelopathy, or in a chronic progressive syndrome ( I -4). In transient myelopathy. symptoms appear within 4 months after therapy and disappear spontaneously within 2-9 months. The chronic progressive syndromes are heterogenous and include classic radiation myelopathy. plexopathy, and neuropathy. A I-are type of neuropathy with isolated motor symptoms, amyotrophy. paresis and fasciculations has been described (4-5). We report a new case, and discuss briefly differential diagnostic considerations, etiological niechanisms, prognosis and therapeutical possibilities. C u e reporr. In 1981, a 26-year-old patient was orchiectomized because of a right-sided seminoma. There was no evidence of metastasis. He received high voltage photon radiotherapy (8 MV). The lumbar and right-sided iliac lymphnodes were irradiated by opposing anterior and posterior fields (2 Gy daily x 1815 days per week). The lumbar target volume included the column from Th 12 to L5 with a field width of 6.7 cm. In addition the patient received electron beam radiotherapy (13 MeV) in the right groin (12 x 13 cm with a triangled block proximal to the inguinal ligament). The daily dose in the inguinal field was 2.9 Gy applied 1 I times. In 1984, the left testicle was removed due to seminoma with histologically verified inguinal lymph metastases but without metastases in the paraaortic region. The patient was retreated with photon radiotherapy (7 MV). The opposing anterior and posterior radiation fields were exposed daily and included the lumbar region from SI to the tenth vertebra (field width: 8.7cm). The risk of damage to the spinal cord was estimated on the basis of the ED formula established by Wara et al. (6, 7). A dose of 32.4 Gy in 0.9 Gy fractions given 9 times a week was chosen as the best compromise between optimal tumor control and risk of cord damage. The interaction interval was 6 h for fractions given on the same day for 16 of the 36 fractions. The dosimetry was reviewed for both treatment series. The total dose i n the lower spinal cord corresponding to the lumbar vertebrae was thus 68.4 Gy. The left iliac inguinal region was irradiated by 20 fractions of 2 Gy ( 5 fractions per week) with opposing fields to the iliac lymph nodes and an anterior field to the inguinal lymph nodes. H e was subsequently treated with Primoteston Depot (180 mg i.m. weekly) and has since remained without sign of tumor or metastasis. About 10 months after the completion of the second radiotherapy series, he noticed impairing strength of the right foot and pain in the right calf muscles after exercise. Similar symptoms appeared 3 years later in the left foot. At this point, a clinical neurological examination revealed only fasciculations in the muscles of both calves and thighs and weak reflexes in both legs. Objective muscle strength and sensibility were unimpaired. Cerebrospinal fluid (CSF) examination showed a total protein of 2.0 g/l, transudative changes at electrophoresis (unspecific protein increase), and normal cytology. EMG was indicative of neurogenic affection with a few fibrillation potentials and nerve velocities were normal. A new examination 4 years later revealed unchanged fasciculations in both legs, amyotrophy in both calves and thighs though the muscular strength was still good. and areflexia. The CSF protein was 2.1 g/l. Peripheral motor and sensory conductions velocities were normal but lower in the tibial posterior nerve than at the previous examination. The F-wave latencies were normal, and the EMG showed polyphasy and decreased amplitude of the motor unit potentials. An MRI examination of the thoracal and lumbo-sacral medulla was normal. Nerve biopsy was not performed. One year later, the clinical status was very much unchanged. The E M G showed more clearly neurogenic affection, the F-wave latencies could not be recorded for the peroneus nerves and were increased for the tibial nerve. There were no sphincter disturbances and sensibility was unimpaired. Discussion. The relevant differential diagnoses in our patient were tumor infiltration in the medulla, amyotrophic lateral sclerosis. motor polyneuropathy and radiation neuropathy. The first possibility was excluded by a normal MRI, clinical and electromyographic examinations excluded the next two. Radiation neuropathy remained the definite diagnosis. The clinical picture in our patient was dominated by amyotrophy, flaccid paresis in the lower limbs, and the absence of sphincter disturbances and sensory symptoms. A similar syndrome was first described by Greenfield & Stark in 1947 ( I ) , and reported later by 7 authors (8-14) bringing the total number of cases to 30. The syndrome has been given different names, which reflects both its rare incidence, and lack of knowledge about the exact localization and nature of the radiation damage. It is mostly described as a postirradiation lower neuron syndrome (PLMNS). The lack of oedema and fibrosis induration,