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X-Linked recessive bulbospinal neuronopathy (X-BSNP) has previously been described as a disease in which the first clinical symptoms which occur concern the motor system. A weakness of the shoulder and pelvic girdle muscles as well as cramps and muscle pain in the proximal limbs are normally found in the early stages.1-3 The onset of X-BSNP generally ranges between the ages of 25 and 50 years; the disorder then shows a slow but continuous progression of symptoms.1 3 An involvement of facial and bulbar musculature with fasciculations and atrophy of these muscles and, therefore, often dysarthria and dysphagia, are common symptoms of an advanced stage.1 3 Nevertheless, life expectancy does not seem to be considerably reduced.1Sensory impairment was reported to be minimal or non-existent.1-3
Pathoanatomical studies showed that a degeneration of both the lower motor and primary sensory neurons represent the underlying pathological process for the clinical symptoms.4 The pathogenetic link between the abnormally expanded CAG trinucleotide repeat in the first exon of the androgen receptor gene which is found in affected patients and the depletion of the anterior horn cells and the primary sensory neurons with consecutive axonal degeneration of the dorsal root fibres has not been established yet.4 5 Although central and peripheral sensory conduction has been shown to be highly abnormal with absent or markedly prolonged sensory action potentials, most of the time the clinical findings of only a little sensory impairment do not correspond well to this electrophysiological constellation.1 3 We report sensory ataxia as the initial clinical symptom in a patient with X-BSNP.
A 63 year old retired journalist felt like “walking on pillows” for the first time when he was 45 years old. During the subsequent years the distally accentuated and symmetric loss of sensibility for touch, temperature, pain, position, and vibration was progressive in the legs—and later—also in the arms. At the age of 48 he noticed fasciculations of the facial muscles and a slow development of a painless, bilateral weakness of the proximal muscles of the lower and upper limbs. No related disease was found in his father's family; nothing is known about the maternal side of his family history.
The clinical examination of the patient showed a severe sensory gait ataxia as well as a dyspraxia of his hands. Other symptoms were a tremor of the hands and occasional spasms of the oral and pharyngeal musculature. The functions of other cranial nerves were normal. Spontaneous fasciculations of the buccal muscles and less often of the proximal and distal limb musculature were seen. Deep tendon reflexes could generally not be detected and there were no pathological reflexes. A proximally accentuated weakness and amyotrophy of the legs and arms as well as a distally accentuated hypaesthesia for all qualities was found. There were no cognitive deficits, cerebellar ataxia, or gynaecomastia.
Laboratory results were not abnormal (including plasma testosterone, follicle stimulating hormone, luteinising hormone, and glucose tolerance) except for a raised creatine kinase (354 U/l). The CSF examination also showed no abnormalities. Motor nerve conduction velocities were only slightly reduced whereas sensory action potentials were absent. Electromyography showed the typical features of chronic denervation in the proximal muscles of the lower and upper limbs as well as in the tongue. Motor evoked potentials showed normal central conduction times but partially prolonged latencies with stimulation of the cervical and lumbal roots. With tibial and median nerve stimulation no somatosensory evoked potentials were found neither at the cervical or lumbal nor at the cortical recording sites. Brain MRI was normal. The genetic analysis showed 42 CAG trinucleotide repeats within the androgen receptor gene (normal length 11–34 repeats), which is a valuable criterion in the diagnosis of X-BSNP.5
The example of our patient shows that the electrophysiological findings of the sensory system may correspond well to the clinical syndrome in X-BSNP. It is not clear why patients with X-BSNP in most cases do not show significant sensory impairment although substantial loss of the primary sensory neuron has been proved. We hope that findings as in this case report may be an incentive for us to work for a better understanding of the problem as to why a specific neuronal degeneration can lead to a less specific pattern of clinical symptoms.
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