Inherited neuropathies

ABSTRACTS PS. Auditory brain-stem potential (ABP) in guinea pigs with chronic relapsing experimental allergic encephalomyelitis. - S. Flechter and J. Vardi (Dept. of Neurology, Shaare Zedek Medical Center, Jerusalem, Israel) Recording of auditory brain-stem potentials (ABPs) has become an important tool in the electrophysiologic test battery employed in the diagnosis of multiple sclerosis (MS). However, there are no pathognomonlc ABP tracings in patients with MS. Chronic relapsing EAE was induced in 20 guinea pigs at the age of 18-21 days. The signs of the disease were scored from grade I to grade IV according to severity. ABPs were recorded in normal as well as in EAE afflicted guinea pigs in the various grades of the disease. A correlation was found between the ABP tracings and the severity of the clinical manifestations of chronic relapsing EAE.

PS. The S E P P 9 / P I 4 amplitude ratio as a means to assess demyelination: a study of 130 M S patients. - L. Garcia Larrea and F. Maugui~re (EEG Dept., Hfipital NeuroIogique, F-69003 Lyon, France) In multiple sclerosis (MS) increased temporal dispersion of afferent impulses due to demyelination reduces amplitudes and increases latencies of the central somatosensory evoked potential (SEP) components without affecting peripheral ones. In demyelination amplitude reduction with increased duration of potentials can occur before latencies reach definitely abnormal values; however, absolute amplitude measurements are difficult to assess due to important intra- and interindividual variations. Far-field (FF) components of the SEP to median nerve stimulation were recorded in 130 patients with probable or definite MS in order to evaluate the diagnostic value of amplitude measurements in this condition. We found that the P9/P14 amjMitude ratio was a sensitive index to assess and quantify amplitude decrease of central F F components. This ratio compares the amplitudes of a peripheral (P9) and a central component (P14) of the SEP and thus is less variable than absolute amplitude measures. It proved to be a robust and reproducible index with a gaussian distribution in normal controls. In our MS patients abnormalities of P9/P14 ratio were in most cases paralleled by abnormal latency values. However, in 9% of the patients the P9/P14 ratio was the only definitely pathological finding. These results suggest that this index might be useful to detect conduction abnormalities in MS patients whose SEP latencies remain in the normal range.

SCs. Intracranial electric fields and stimulation of the motor cortex. - F. Grandori * and P.M. Rossini * * ( * Centro di Teoria dei Sistemi C.N.R., Politecnico di Mllano, Milan, and * * Neurofisiologia Clinica, H Universith di Roma, Rome, Italy)

Some techniques of stimulation of human unexposed motor cortex are studied with a mathematical model accounting for

S121 the basic electrical properties of the human head. The model consists of 13 concentric conducting spherical media, with different conductivity, representing the scalp, the skull and the brain tissues, respectively. The model is energized by currents applied on the surface of the outermost sphere; intracranial potential fields and current densities are computed at various depths and locations. Although several modeling assumptions are valid only at a first approximation, this approach is shown to be a. useful tool to investigate some aspects of great concern for the use of these techniques. Analysis of the model results confirms several experimental observations in that intracranial potential distributions seem to be rather insensitive to intrasubjective variability of the electrical and geometrical properties of the tissues. Data are also presented about the influence of electrode separation, with 2 electrodes, on the spread of currents at various depths and locations: in deep regions - depth greater than some 2-2.5 cm from the surface of the innermost sphere - the larger the separation the greater is the momentum of the current density vector, along the axis of symmetry of the electrode montage. For depth less than 2-2.5 cm the situation is reversed. Under electrodes, the smaller the separation the lower is the current density.

SY. Inherited neuropathies. - A.E. Harding (Institute of Neurology, Queen Square, London W C I N 3BG, U.K.)

The inherited neuropathies are a complex heterogeneous group of disorders. In some peripheral nerve dysfunctions neuropathy is the only manifestation of the underlying gene mutation, whereas in others neuropathy is one feature of a multisystem disease. Inherited neuropathies with a known metabolic basis can be conveniently separated from those of unknown etiology. This communication will deal with 2 main themes: (i) the increasing clinical spectrum of inherited metabolic disorders affecting peripheral nerve; and (ii) the application of the 'new genetics' to inherited neuropathy.

PS. Chronic distal spinal muscular atrophy in adults (involving the hands) - clinical and electrophysiological studies. J. l-lromada (City Hospital, Dept. of Neurology, Nemocnicnl 20, Czechoslovakia)

Spinal muscular atrophies in adults are a very heterogenous group of disorders in which the primary defect is degeneration of the anterior horn cells of the spinal cord and eventually of the bulbar motor nuclei. They differ markedly in the course and extent of the involvement. In chronic spinal muscular atrophy in the beginning of the disease there is a quick onset of the symptoms - localized atrophies on the limbs, or in the area of cranial nerves (focal motor neuron disease). The course then progresses very slowly. The chronic form usually involves proximal muscles of the limbs; the involvement of the distal muscles and above all localized small muscle atrophies of the