Peripheral neuropathy in spinocerebellar degenerations

Peripheral nerve involvement in hereditary cerebellar and multisystem degenerative disorders

Hereditary ataxias (HA) encompass an increasing number of degenerative disorders characterized by progressive cerebellar ataxia usually accompanied by extracerebellar semeiology including peripheral nerve involvement. Classically, HA were classified according to their pathological hallmark comprising three main forms: (1) spinal form predominantly with degeneration of spinocerebellar tracts, posterior columns, and pyramidal tracts (Friedreich's ataxia, FA); (2) olivopontocerebellar atrophy (OPCA); and (3) cortical cerebellar atrophy (CCA). In the 1980s Harding proposed a clinico-genetic classification based upon age of onset, modality of transmission, and clinical semeiology. The main categories in this classification were as follows: (1) early onset cerebellar ataxia (EOCA) with age of onset below 25 years and usually with autosomal recessive (AR) transmission (this group encompasses FA and syndromes different from FA); (2) autosomal dominant cerebellar ataxia (ADCA) with adult onset and with either cerebellar-plus syndrome or pure cerebellar semeiology; and (3) idiopathic late onset onset cerebellar ataxia (ILOCA). With the advent of molecular genetics, the nosology of HA has been in a state of constant flux. At present EOCA comprises at least 17 genotypes (designated with the acronym of ARCA derived from AR cerebellar ataxia), whereas under the umbrella of ADCA 30 genotypes have been reported. In this chapter we will review peripheral nerve involvement in classical pathological entities (OPCA and CCA), ARCA, ADCA, and ILOCA paying special attention to the most prevalent syndromes in each category. As a general rule, nerve involvement is relatively common in any form of ataxia except ILOCA, the most common pattern being either sensory or sensorimotor neuronopathy with a dying-back process. An exception to this rule is AR spastic ataxia of Charlevoix-Saguenay where nerve conduction studies show the characteristic pattern of intermediate neuropathy implying that sacsin mutation causes both axonal and Schwann cell dysfunction.

Severe back pain following epidural analgesia in patients with spinocerebellar ataxia: a report of two cases

Two patients with spinocerebellar ataxia received epidural analgesia with no exacerbation of their symptoms. The patients developed transient, but extremely severe, low back pain as a result of the epidural analgesia.

Multimodal neurophysiological study of SCA2 and SCA3 autosomal dominant hereditary spinocerebellar ataxias

BACKGROUND

The spinocerebellar ataxias (SCA) are a group of genetic neurodegenerative diseases, clinically and pathologically heterogeneous, characterized by slowly progressive cerebellar ataxia.

OBJECTIVE

To identify the neural pathways affected neurophysiologically, correlate the findings with the size of CAG expansion and determine the contribution of neurophysiological studies in the differential diagnosis of the two most prevalent genotypes in Spain, SCA2 and SCA3.

METHOD

We examined 10 SCA2 and 12 SCA3 patients by electromyography, electroneurography motor and sensory, multimodal evoked potentials, transcranial magnetic stimulation, blink reflex and masseter reflex. In the statistical analysis linear regression studies were performed, and the, Spearman correlation coefficient and nonparametric test U of Mann-Whitney calculated.

RESULTS

We detected the presence of a predominantly sensory neuropathy in most SCA2 patients and in a minority of SCA3 patients; the central somatosensory pathway showed significant defects in both populations. We recorded a high incidence of brain-stem electrophysiological abnormalities in SCA2 patients; in particular, the masseter reflex was abnormal in all SCA2 patients, remaining intact in all SCA3 patients. The study of cortico-spinal pathway showed a greater percentage of abnormalities in both populations than in previous studies.

CONCLUSION

SCA2 is a model of sensory neuronopathy with central and peripheral axonopathy. Studies of brain-stem pathways show a higher incidence of abnormalities in SCA2 patients. SCA3 patients show major changes in the central somatosensory pathway with relative normality of the electroneurography. The masseter reflex was the most useful test in the differential diagnosis between both genotypes.

Balance control in Sensory Neuron Disease

OBJECTIVE

Balance control under static and dynamic conditions was assessed in patients with Sensory Neuron Disease (SND) in order to shed further light on the pathophysiology of ataxia.

METHODS

Fourteen patients with diabetic polyneuropathy and 11 with SND underwent clinical and neurophysiological evaluation, stabilometric recording of body sway during quiet stance with and without vision, stereometric analysis of body segment displacement while riding a platform translating in anterior-posterior direction with and without vision (dynamic condition), and EMG recording of leg muscle responses to abrupt stance perturbation produced by rotation of a supporting platform. The findings were compared to those of age matched normal subjects.

RESULTS

Clinical and neurophysiological evaluation revealed a more severe motor impairment in patients with diabetes than SND, while sensory impairment was superimposable. Some patients with SND had vestibular dysfunction of diverse severity. Body sway during stance was larger in patients with SND than diabetes with and without vision. In the stance perturbation condition, the latency of the long-loop EMG response to platform rotation was disproportionately increased with respect to the spinal response in the SND but not in diabetic patients. Under dynamic condition, patients with SND oscillated more than diabetic patients and several of them easily lost balance with eyes closed.

CONCLUSIONS

Patients with SND show severe unsteadiness under both static and dynamic conditions, particularly with eyes closed. The patchy sensory loss of SND, disrupting sensation from territories other than the lower limbs and possibly including the vestibular nerve, could be responsible for this instability. Ataxia is correlated to the abnormal latency of the muscle responses to stance perturbation. Since increased response latencies cannot be attributed to a vestibular deficit, the deterioration of equilibrium control would be ascribed mainly to the degeneration of the central branch of the afferent fibres.

SIGNIFICANCE

Measures of body balance under quiet stance and dynamic conditions can provide relevant diagnostic information as to the pathophysiology and severity of ataxia and viability of the central branch of the sensory fibres, and help in separating patients with peripheral neuropathy from patients with loss of sensory neurones.

Acute sensory neuronopathy as the presenting symptom of Sjögren’s syndrome

Sensory neuronopathy associated with Sjögren's syndrome (SS) usually has a subacute or chronic onset. We report the case of a 37-year-old woman who presented with an unusual hyperacute form of SS ganglionopathy. She initially developed paresthesias of her fingertips and rapidly became severely ataxic. Nerve conduction studies revealed abnormal sensory but normal motor functions. Lip biopsy showed findings consistent with SS. Sural nerve biopsy showed severe axonal loss. The patient showed modest improvement with immunosuppressive therapies.

Sensory neuron diseases

Sensory neuron diseases (SND) are a distinct subgroup of peripheral-nervous-system diseases, first acknowledged in 1948. Acquired SND have a subacute or chronic course and are associated with systemic immune-mediated diseases, vitamin intoxication or deficiency, neurotoxic drugs, and life-threatening diseases such as cancer. SND are commonly idiopathic but can be genetic diseases; the latter tend to involve subtypes of sensory neurons and are associated with certain clinical pictures. The loss of sensory neurons in dorsal root ganglia causes the degeneration of short and long peripheral axons and central sensory projections in the posterior columns. This pathological process leads to a pattern of sensory nerve degeneration that is not length dependent and explains distinct clinical and neurophysiological abnormalities. Here we propose a comprehensive approach to the diagnosis of acquired and hereditary SND and discuss clinical, genetic, neurophysiological, neuroradiological, and neuropathological assessments.

Autosomal dominant sensory/motor neuropathy with Ataxia (SMNA): Linkage to chromosome 7q22-q32

The autosomal dominant (AD) spinocerebellar ataxias (SCAs) and hereditary sensory neuropathies (HSN) are heterogeneous disorders characterized by variable clinical, electrophysiological, and neuropathological profiles. The SCAs are clinically characterized by slowly progressive incoordination of gait often associated with poor coordination of hands, speech, and eyes. Peripheral neuropathy is not a frequent part of the SCA syndrome. In contrast, the HSNs are primarily characterized by progressive sensory loss. There is substantial clinical overlap between the various SCAs and the various HSNs, and they often cannot be differentiated on the basis of clinical or neuro-imaging studies. We have identified a five-generation American family of Irish ancestry with a unique neurological disorder displaying an AD pattern of inheritance. There was variable expressivity and severity of symptoms including sensory loss, ataxia, pyramidal tract signs, and muscle weakness. Nerve conduction studies were consistent with a sensory axonal neuropathy. Muscle biopsy revealed neurogenic atrophy and brain MRI showed mild cerebellar atrophy. To identify the responsible locus we pursued a whole genome linkage analysis. After analyzing 114 markers, linkage to D7S486 was detected with a two point LOD score of 4.79 at theta = 0.00. Evaluation of additional markers in the region provided a maximum LOD score of 6.36 at theta = 0.00 for marker D7S2554. Haplotype analysis delimited an approximately 14-cM region at 7q22-q32 between markers D7S2418 and D7S1804 cosegregating with the disease. Because this disorder does not easily fall into either the SCA or HSN categories, it is designated sensory/motor neuropathy with ataxia (SMNA).

Polyneuropathy in autosomal dominant cerebellar ataxias: phenotype-genotype correlation

Autosomal dominant cerebellar ataxias (ADCAs) are clinically and genetically heterogeneous neurodegenerative disorders. The aim of this study was to evaluate electrophysiologically peripheral nervous system involvement in each of the groups studied and its correlation with the number of CAG repeats. Forty patients with ADCA were clinically and electrophysiologically investigated. Thirty-five patients belonged to the ADCA type I group (SCA1, 12; SCA2, 10; SCA3, 13) and five to the ADCA type II group. Axonal sensory or sensorimotor polyneuropathy was found in 42% of the SCA1 patients, 80% of the SCA2 patients, and 54% of the SCA3 patients, whereas electrophysiological studies were normal in all those with ADCA type II. The number of CAG repeats was significantly higher in SCA1 patients with polyneuropathy than in those without polyneuropathy (P = 0.01), whereas the reverse was observed in SCA3/MJD (Machado-Joseph disease) patients (P = 0.05). We conclude that axonal polyneuropathy is often associated with ADCA type I, but its frequency varies according to factors such as the locus responsible and the number of CAG repeats.

Bullous pemphigoid associated with Shy-Drager syndrome

We report a patient with Shy-Drager syndrome who developed multiple tense blisters mainly on the extremities. Circulating anti-basement membrane zone autoantibodies were detected by the indirect immunofluorescence method. Immunoblot analysis using normal human epidermal extracts demonstrated that this patient's serum reacted only with 230 kD bullous pemphigoid antigen (BPAG1). Concerning the pathoetiology of the association of bullous pemphigoid and Shy-Drager syndrome, we discuss a sequence similarity between BPAG1 and dystonin, a candidate gene for dystonia musculorum.

Sensory neuropathies including painful and toxic neuropathies

In most peripheral neuropathies, dysfunction of motor and sensory nerve fibres is present. However, in some of them either pattern may predominate or be exclusively present. In this review we describe the clinical characteristics of sensory neuropathies, with emphasis on their possible causes. Guidelines are given for the diagnostic approach in these patients and, where possible, suggestions are given for treatment, including symptomatic treatment of painful neuropathies.

Electrophysiological findings in a Danish family with Machado-Joseph disease

Machado-Joseph disease (MJD) is a neurodegenerative disorder with autosomal dominant inheritance, We have carried out electrophysiological studies in 8 individuals belonging to a Danish family with several affected members. Five had an expanded trinucleotide (CAG) repeat sequence in the MJD1 gene on chromosome 14 indicating MJD, while 3 unaffected individuals had normal repeat lengths. Three individuals with repeat expansion had clinical symptoms and signs of the Machado or "type III" phenotype, whereas 2 had slight symptoms and signs only, Electrophysiological evaluation included visual, somatosensory, and auditory brain stem evoked potentials, quantitative electromyography, and nerve conduction studies. In the patients with clinical MJD, evoked potential studies showed multimodal abnormalities, electromyography showed neurogenic changes, and nerve conduction studies showed signs of severe loss of motor and sensory nerve fibers. Of the 2 patients with slight symptoms and signs, 1 had evidence of peripheral and central affection, while the other had slight signs of a central affection. This study provides insight into the distribution and character of electrophysiological abnormalities in MJD of putative importance for an understanding of the pathogenesis of the disease, and for monitoring disease progress, or the outcome of a possible treatment.

Transcranial magnetic stimulation in multiple system and late onset cerebellar atrophies

Central motor conduction time (CMCT) after transcranial magnetic stimulation (TMS) of the cortex, electromyography and nerve conduction velocity were performed in 24 patients with multiple system (MSA) and late onset cerebellar atrophy (LOCA) (often olivopontocerebellar atrophy--OPCA -). CMCT was abnormal in 7 patients with OPCA and one with LOCA. CMCT abnormalities (43% of cases) and increased threshold (68%) were more often found within OPCA group than in another multisystem atrophy and LOCA. Reduction in amplitude of the response after TMS was significantly correlated with cerebral hemispheres's atrophy. Increased threshold was correlated with upper vermal hemisphere atrophy and enlargement of the fourth ventricle. Electrophysiologic signs of mixed peripheral neuropathy were found in 8 patients. TMS abnormalities were not related to peripheral nerve involvement. Marked variation in CMCT suggests heterogeneity in these diseases. However, the percentage of CMCT abnormalities in OPCA group suggests that TMS seems to play a role in the neurophysiological diagnosis of these heterogeneous disorders.

The mouse dystonia musculorum gene is a neural isoform of bullous pemphigoid antigen 1

Dystonia musculorum (dt) is a hereditary neurodegenerative disease in mice that leads to a sensory ataxia. We describe cloning of a candidate dt gene, dystonin, that is predominantly expressed in the dorsal root ganglia and other sites of neurodegeneration in dt mice. Dystonin encodes an N-terminal actin binding domain and a C-terminal portion comprised of the hemidesmosomal protein, bullous pemphigoid antigen 1 (bpag1). dt and bpag1 are part of the same transcription unit which is partially deleted in a transgenic strain of mice, Tg4, that harbours an insertional mutation at the dt locus, and in mice that carry a spontaneous dt mutation, dtAlb. We also demonstrate abnormal dystonin transcripts in a second dt mutant, dt24J. We conclude that mutations in the dystonin gene are the primary genetic lesion in dt mice.

Investigation of peripheral neuropathy

Images

Sensory neuropathy in infantile onset spinocerebellar ataxia (IOSCA)

Infantile onset spinocerebellar ataxia with sensory neuropathy is a new, inherited multisystem disorder discovered in 19 Finnish patients. In order to define the neuropathy of the disease, we measured sensory nerve action potentials and nerve conduction velocities in 18 patients, and recorded somatosensory evoked potentials (SEP) in 10 patients and performed a sural nerve biopsy in 13 patients. The fixed and teased nerve fascicles were examined by light and electron microscopy, and the whole transverse section of a nerve fascicle was photographed and enlarged for morphometric measurements. Our investigation revealed an early onset, rapidly progressive axonal neuropathy: the sensory action potentials were decreased after the age of 2 and a severe loss of mainly large myelinated fibers was found.

Hereditary sensory neuropathies

Hereditary sensory neuropathies have not shared in the major advances that have taken place in the molecular genetics of the hereditary demyelinating motor and sensory neuropathies. Thus far, classification depends upon their mode of inheritance and clinical features. The delineation of the various clinical syndromes is still not complete. This is a necessary preliminary to establishing the genetic basis of these neuropathies. The hereditary sensory neuropathies can be accordingly grouped into those with predominantly sensory and some associated autonomic features and those in which a sensory neuropathy is part of a spinocerebellar degeneration or other multisystem degeneration.

Is early onset cerebellar ataxia with retained tendon reflexes identifiable by electrophysiologic and histologic profile? A comparison with Friedreich's ataxia

An electrophysiologic and histologic study was performed on 18 patients affected by early onset cerebellar ataxia with retained tendon reflexes (EOCA). Sensory and motor conduction velocity (SCV, MCV) was measured along peripheral nerves in all patients, somatosensory (SSEP) and brainstem auditory evoked potentials (BAEP) were recorded in 13; cortical stimulation (CS) in 12, and sural nerve biopsy in 4 patients were also performed. The results as a whole allow a division of EOCA patients into 2 groups: with (7 patients) and without (11 patients) peripheral neuropathy. Among EOCA patients with neuropathy a differential diagnosis with Friedreich's disease patients was not possible according to BAEPs and CS, while SSEPs could differentiate 2 out 5 patients in whom they were performed.

Cryptogenetic polyneuropathies: an out-patient follow-up study

An out-patient follow-up study of 41 patients suffering from cryptogenetic PNP was performed: 19 (46%) had a symmetric-paretic; 15 (37%) a symmetric-sensory, 4 (10%) an asymmetric type polyneuropathy and 3 (7%) presented with mononeuropathia multiplex; 12 of 41 (29%) unclassified PNP could be clarified. Of the remaining 29 unsolved cases, 14 (48%) formed a homogeneous subgroup sharing specific criteria: primary, axonal type degeneration; slowly progressing clinical course reaching a plateau; low disability status; onset between the age of 45-65. We concluded that out-patient re-evaluation of cryptogenetic PNP yields improved diagnosis. Hereditary and immune-mediated PNP exhibit specific diagnostic problems and account for a large portion of the cryptogenetic PNP.

Autonomic involvement in extrapyramidal and cerebellar disorders

We reviewed the clinical and autonomic features of all patients with extrapyramidal and cerebellar disorders studied in the Mayo Autonomic Reflex Laboratory from 1983 to 1989. Patients were grouped into the following categories (number in parentheses): Parkinson's disease (35); parkinsonism-plus (54); multiple system atrophy (75); hereditary multisystem degenerations (eleven); progressive supranuclear palsy (32); non-familial cerebellar degeneration (eleven); nonspecific sporadic multisystem degeneration (73). Severe autonomic failure occurred in 97% of patients with multiple system atrophy and 53% of the nonspecific sporadic multisystem degeneration patients respectively. Autonomic involvement was mild or absent in Parkinson's disease while parkinsonism-plus and non-familial cerebellar degeneration patients had moderate autonomic failure. Orthostatic blood pressure reduction, percentage of anhidrosis on thermoregulatory sweat test, quantitative sudomotor axon reflex test, forearm response and heart rate response to deep breathing strongly regressed with severity. A response to levodopa treatment in patients with parkinsonism was more likely if cerebellar signs and cognitive deficits were absent. The presence of levodopa induced dyskinesia was also a marker for a clinically favourable levodopa response. We conclude that there is a spectrum of autonomic involvement in these degenerative disorders and that autonomic studies are useful in separating them and monitoring their course.

Utility of short-latency evoked potentials in the classification of progressive, early onset cerebellar ataxias

In recent years, several authors have proposed new classifications of inherited ataxias, some of them being based on systematic clinical studies of large groups of patients. This methodic approach has led to the identification of new types of ataxias and helped the development of molecular biology research in these diseases. Up to now, nerve conduction velocity and evoked potential studies have not been considered in the classification of hereditary ataxias. We have studied the results of short latency evoked potentials in 102 patients affected by a early onset, progressive cerebellar ataxia. Based on the results of this study and a review of the literature on this subject, we will evaluate the utility of nerve conduction velocity and evoked potential recordings in the classification of this group of diseases.

Motor dysfunction in olivopontocerebellar atrophy is related to cerebral metabolic rate studied with positron emission tomography

We compared the severity of motor dysfunction with local cerebral metabolic rates for glucose (lCMRGlc) and the degree of tissue atrophy in 30 patients with olivopontocerebellar atrophy (OPCA). We devised a scale to quantitate the degree of ataxia in the neurological examinations. lCMRGlc was measured with 18F-2-fluoro-2-deoxy-D-glucose and positron emission tomography (PET). Tissue atrophy was assessed by visual rating of computed tomographic scans. PET studies revealed marked hypometabolism in the cerebellar vermis, cerebellar hemispheres, and brainstem of OPCA patients compared with 30 control subjects. A significant correlation was found between severity of motor impairment and lCMRGlc within the cerebellar vermis, both cerebellar hemispheres, and the brainstem. A significant but weaker relationship was noted between the degree of tissue atrophy in these regions and clinical severity. Partial correlation analysis revealed that motor dysfunction in OPCA correlated more strongly with lCMRGlc than with the amount of tissue atrophy. These results suggest that the clinical manifestations of OPCA are more closely related to the metabolic state of the tissue than to the structural changes in the cerebellum.

Peripheral neuropathy in late onset spinocerebellar ataxia

We studied 10 patients with late onset spinocerebellar ataxia including electrophysiological and muscle biopsy examinations. Nerve conduction studies of eight patients revealed axonal neuropathy, and six cases also showed signs of the involvement of the lower motor neuron. In 9 patients quantitative analysis of single motor unit potentials (MUPs) of the tibialis anterior or biceps brachii muscles showed mild to severe neuropathic changes and in all 10 patients the histopathological examination of the tibialis anterior showed mild to severe neuropathic changes. Neither nerve conduction studies, quantitative MUP analysis, nor histological findings of the muscle were related to the severity of duration of the disease.

Cerebellar and brainstem hypometabolism in olivopontocerebellar atrophy detected with positron emission tomography

We studied local cerebral metabolic rates for glucose (1CMRglc) with 18F-2-fluoro-2-deoxy-D-glucose and positron emission tomography (PET) in 30 patients with olivopontocerebellar atrophy (OPCA) and 30 age-matched control subjects without neurological disease. The diagnosis of OPCA was based on the history and physical findings and on the exclusion of other causes of cerebellar ataxia by means of laboratory investigations. Computed tomographic scans revealed some degree of atrophy of the cerebellum in most patients with OPCA, and many also had atrophy of the brainstem. PET studies in these patients revealed significant hypometabolism in the cerebellar hemispheres, cerebellar vermis, and brainstem in comparison with the normal control subjects. A significant relationship was found between the degree of atrophy and the level of 1CMRglc in the cerebellum and brainstem. Nevertheless, several patients had minimal atrophy and substantially reduced 1CMRglc, suggesting that atrophy does not fully account for the finding of hypometabolism. 1CMRglc was within normal limits for the thalamus and cerebral cortex. The data suggest that PET/1CMRglc may be useful as a diagnostic test in patients with the adult onset of cerebellar ataxia.

Involvement of somatosensory and visual pathways in late onset ataxia

Nerve conduction studies, median nerve somatosensory (SEPs) and pattern-reversal visual evoked potentials (VEPs) were recorded in 10 patients with late onset ataxia. Nine patients had dysfunction of somatosensory pathways, eight of them axonal polyneuropathy in nerve conduction measurements, and four had also impaired impulse conduction along the visual pathways. Abnormalities in records of evoked potentials occurred as prolonged latencies rather than reduced amplitudes. The observed dysfunction of peripheral and central pathways was not related to the duration or the severity of the clinical involvement by the disease. It is emphasized, however, that there seemed to be a relationship between the prolonged SEP latencies and the impaired peripheral nerve conduction values and between the diminished VEP amplitudes and the most delayed VEP latencies.

Hypertrophic neuropathy in spinocerebellar degeneration. Morphological study of the superficial peroneal nerve in fourteen cases

Fourteen patients belonging to eight families were studied. At least one member of each family presented a clinical picture of spinocerebellar degeneration (SCD) and lowered motor nerve conduction velocity (MNCV). Muscular atrophy of the Charcot-Marie-Tooth type was found in 11 cases. The average MNCV of the median nerve was less than half the value in the controls (P less than 0.001). Morphometric analysis of the superficial peroneal nerve showed a considerable reduction (P less than 0.001) in myelinated fibres, primarily those of large diameter (P less than 0.001), a high average density of onion bulb formations, and a large percentage (P less than 0.001) of teased fibres showing aspects of segmental demyelination, with or without remyelination. These results indicate the presence of a hypertrophic neuropathy (HN) associated with the SCD. In most cases, this HN bore the electrophysiological and morphological features of type I hereditary motor and sensory neuropathy. In certain cases, however, there was an individual and intra-familial discordance of the electrophysiological and histological aspects, which may correspond to a difference in phenotypic expression, or to mutant genes. It is possible that a single disease is involved, assuming the clinical appearance of both SCD and HN, the biochemical support of which remains to be determined.

Sensory and motor peripheral neuropathy in olivopontocerebellar atrophy

We report the findings of an electrophysiological study in 9 patients affected by olivopontocerebellar atrophy, 4 with a dominant form and 5 with a sporadic form. Superficial peroneal nerve biopsy was obtained from 2 patients. The electrophysiological alterations were signs of collateral reinnervation and loss of motor units, decrease in sensory potential amplitude and increase in distal motor latency. Only a slight reduction in motor and sensory conduction velocity was observed in some cases. Nerve biopsy showed slight reduction of the number of myelinated fibres. In the first case, fibre diameter distribution was unimodal, due to reduction of myelinated fibres of large diameter, in the second case there was no significant alteration of the fibre distribution. In both cases short internodes were present with no signs of segmental demyelination, remyelination or axonal degeneration. The alterations observed in the peripheral nervous system are probably secondary to a lesion of the posterior root ganglion and the anterior horn cell in the spinal cord.

Mitochondrial dysfunction and spinocerebellar degenerations

A simplified classification of the spinocerebellar degenerations is proposed. Axonal ataxias include Friedreich's ataxia and other conditions involving, primarily, neurons with very long axons. Multiple system degenerations include the various olivopontocerebellar atrophies and related disorders. Ataxic encephalopathies are diffuse diseases of the nervous system in which ataxia is a prominent clinical feature. Several lines of data suggest that mitochondrial damage is a common mechanism in the spinocerebellar degenerations. Reasonable pathophysiological mechanisms can be invoked, linking mitochondrial damage to the observed pathologies (including the many cases of intermediate on variant forms).

The peripheral neuropathy in Machado-Joseph disease

Peripheral nerve biopsies were taken from 11 patients with Machado-Joseph disease (MJD), a heredo-degenerative disease within the group of autosomal dominant ataxias. On the basis of the clinical symptoms, 2 patients were found to suffer from type I, 4 from type II and 5 from type III. All cases shared the same pathological features, which consisted of a reduction in density of myelinated and unmyelinated fibres and an increase in endoneurial collagen. It was also observed that some Schwann cells were not related to axons, whilst others showed numerous budding processes. The intensity of the changes varied considerably: it was mild in type I and II and severe in type III. Peripheral nerve changes in MJD are compared with those previously described in other forms of heredo-ataxias. It is concluded that involvement of peripheral nerves is a significant feature in this group of diseases and that peripheral nerve biopsy could be useful in the identification of the subtypes of MJD.

The peripheral neuropathy of vitamin B12 deficiency

Nerve conduction studies and sural nerve biopsy were performed on three patients with vitamin B12 deficiency and symptoms of peripheral neuropathy. The pathological findings were those of axonal degeneration; there was no evidence of demyelination. The patients were reviewed at intervals of 5-15 years commencement of treatment; progression of the neuropathy had been arrested by treatment, but in all cases residual neurological abnormalities persisted. In one patient with autonomic neuropathy, the postural hypotension resolved rapidly and fully with treatment.

Chronic polyneuropathy of undetermined cause

The case histories of 519 patients with peripheral neuropathy on whom sural nerve biopsy had been performed were reviewed. In 67 patients (50 males, 17 females) (13%) who had symptoms of a symmetrical polyneuropathy for more than one year, the cause remained undiagnosed in spite of intensive investigation. Patients with inflammatory neuropathy were not included, but represented 17% of the whole series. The mean age of onset of symptoms was 50.6 years, and the median time from onset of symptoms to initial investigation was 2 years. Males were affected more commonly than females in a ratio of 3:1. The clinical features in 43 patients were those of a mixed motor and sensory neuropathy, in 17 patients a predominantly sensory neuropathy and in 7 patients a predominantly motor neuropathy. The mean CSF protein was 0.73 g/l and in only six patients was it greater than 1 g/l. Nerve conduction studies most commonly demonstrated mild slowing of motor conduction and impairment of sensory conduction. The usual pathological changes on sural nerve biopsy were those of chronic axonal degeneration. Forty seven patients (70%) were re-examined at intervals of time which ranged from 4 months to 12 years after their initial presentation and nerve biopsy (median, 3 years). As a group, they were only mildly disabled, the condition had a very slowly progressive course and there had been little change in their disability. A possible aetiological factor was found in 17 of the 47 patients (36%) and included malignancy, alcoholism, and benign paraproteinaemia. It is concluded that with intensive investigation the cause of chronic polyneuropathy of duration greater than one year remains undetermined in only about 13% of patients and that continued follow-up is worthwhile since a diagnosis may be established on re-examination.

Electromyography and nerve conduction study in autosomal dominant olivopontocerebellar atrophy

Electromyographic examination and studies of motor and sensory conduction velocities were performed in 11 patients with a presumptive diagnosis of olivopontocerebellar atrophy with autosomal dominant transmission. Peripheral nervous system involvement was shown in eight. In two patients with early onset of disease, electrophysiological alterations clearly pointed to severe axonal degeneration, whereas in six they were compatible with slight demyelination.

Retinitis pigmentosa, ataxia, and peripheral neuropathy

The clinical features of four patients with retinitis pigmentosa, ataxia and peripheral neuropathy but with no increase in serum phytanic acid are reported. Three patients also had sensorineural deafness and radiological evidence of cerebellar atrophy. Nerve conduction studies revealed abnormalities of sensory conduction and normal or only mild slowing of motor conduction velocity. Sural nerve biopsy demonstrated a reduction in the density of myelinated fibres. There were no onion bulb formations. These cases clinically resemble Refsum's disease, but differ in having no detectable biochemical abnormality, and a peripheral neuropathy which is not hypertrophic in type. They may represent unusual cases of spinocerebellar degeneration.