THE CLASSIFICATION OF DISORDERS OF SPEECH

E. Bay

(Neurologische Universitatsklinik, Dusseldorf)

In face of the large and varied body of experience represented by the different types of aphasic disorders, it is imperative to divide it into smaller and more uniform groups, that is, to classify according to certain principles. This is necessary for the scientific management of the material, as well as for mutual communication.

A logical classification is only feasible on a theory based upon the underlying pattern of relations, e.g. on a theory of aphasia. Probably contemporary aphasiologists will not agree upon a precise theory of aphasia and we can, therefore, scarcely expect to agree upon an exact and wholly satisfactory system of classification. Regarding the most unsatisfactory system which is employed at present, however, we should be able to effect some agreed improvement.

The current classification comprises so many biassed and inconsist­ent features that it mus lead to misunderstandings and embarrass­ment. In fact, it is largely responsible for the confusion and dispute of past and contemporary aphasiology. If we could only eliminate some of its errors and inconsistencies, we should at least be able to agree upon certain generalities and fundamentals of classification, in order to reduce the level of mutual misunderstanding.

The usual classification of aphasic disorders into a multiplicity of cortical and subcortical, motor and sensory, amnesic, conduction, and other aphasias, is based upon the theory that language is the result of numerous elementary functions connected by reflexes, and localized within isolated cortical areas. There are now scarcely any contemporary adherents to this theory, yet many aphasiologists try to retain this classification simply because of its convenience, inde­pendent of the consequences of the underlying theory. This is

The classification of disorders of speech 27

impossible because that particular kind of classification, in fact, reintroduces essential parts of the seemingly discarded theory. For our present purposes, which are mainly pragmatical, however, we need not consider these theoretical implications in detail. Rather, I would prefer to concentrate my criticism upon a number of practical points.

A workable system of classification must divide a multitude of individual cases into different groups of the system. The efficiency of the system depends upon plain and unequivocal criteria for the distinction of its different items. Considering under these aspects the different labels of motor or sensory, Broca's and Wernicke's, amnesic, nominal or any other special type of aphasia, we find that both description and definition of these individual forms vary widely from author to author - unless he prefers to reject all definitions - and that these definitions are overdetermined and, therefore, equivocal.

For instance, one essential characteristic of Broca's aphasia is a severe disorder of speaking for all kinds of verbal expression including repetition and reciting of serials which cannot be explained on the basis of a concomitant dysarthria. Other determinants of the same motor aphasia are a prevalence of expressive, compared with receptive, disorders or the occurrence of literal paraphasias and telegramatic style of speech. All these symptoms depend on different pathogenetic variables and may, therefore, appear mutually discordant, and then the diagnosis would depend upon which feature is considered all­important.

In pertinent cases from the literature it is easy to demonstrate that the diagnosis of motor aphasia is attached to disorders of essen­tially different pathogenetic patterns. Lord Brain lately repeated the old doubts whether any of Broca's patients suffered from Broca's aphasia. In all other classical types of aphasia the problem is essentially the same.

In addition to its intrinsic ambiguity this scheme of classification makes use of some criteria for differential classification which are particularly apt to introduce arbitrariness and confusion into the diagnostic procedure.

A major and ever-present source of bias is to base classification on the comparison between different types of normal or abnormal behavior: for instance, defining motor aphasia by the predominance of expressive over receptive disorders means to offset expressive against receptive performances, e.g. to compare troubles of naming with

28 E. Bay

difficulties in verbal comprehension. But these are quite differently patterned performances; they lack a common frame of reference which would be the first prerequisite for a comparison. Hence, the commonly employed phrase of a "comparatively severe" or a "comparatively mild" disorder of this or that function as a criterion of classification leads to an unlimited arbitrariness.

Another source of bias and confusion is the unwarranted elimina­tion of so-called" insignificant" troubles. As an example I may again quote motor aphasia, now defined as a severe trouble of speaking which is not explained by any primary impairment of the articulatory muscles (e.g., dysarthria). This definition would be adequate so long as there is no primary motor involvement at all. However, the vast majority of pertinent cases admittedly displays a motor impairment as shown by oral apraxia. Then, of course, it is open to doubt how far such motor impairment does or does not influence articulation and speaking. This question can only be answered by further investigations which have never been made, as far as I know. Instead, the problem is allegedly solved on the basis of preconceived theoretical assumptions.

This type of argument is widely used in the conventional schemes of classification. It certainly disposes of any facts which contradict the theory, yet, it precludes any hope for a general accord upon the subject of classification.

In order to attain a reliable and generally acceptable classification, it is necessary to consider some fundamental conditions.

First of all, we must not promote classification further than we are able to classify, i.e., to distinguish clearly and reliably between different classes. It is safer to divide into few but clearly discernible groups, than into many groups which cannot be rightly distinguished. The classical scheme which is based on a theory rather than on experience by far exceeds the possibilities of practicable and unequi­vocal discrimination.

In this respect, the procedure of Weisenburg and McBride of differentiating between "predominantly expressive" and "predomi­nantly receptive" disorders is ostensibly superior to the classical system. Unfortunately, the classification of Weisenburg and McBride still employs the ambiguous expressive versus receptive formula and, of course, their two groups do not represent homogenous morbid patterns.

The classification of disorders of speech 29

Furthermore, each constituent of the classification system needs to be defined on the basis of a single, unequivocal property of pattern. Over-determination by several properties must result in embarrassment as soon as the different properties (or patterns) are independently va­riable.

To avoid arbitrary comparison of incomparable items, qualitative differential diagnosis should be exclusively based on the net presence or absence of specific symptoms, i.e. on a clear "yes" or "no" as op­posed to "more" or "less." The latter distinctions can be used only quantitatively to differentiate a severe case from a slight one, com­paring identical functions in different patients.

This principle also excludes classificatory procedures according to the following method: Symptom A admittedly depends upon symptom B, yet, preconceived opinion states that it cannot be "explained" by symptom B and, therefore, a "specific" disorder of A is postulated and becomes an essential determinant of classification. (Such is, for instance, the relation between expressive verbal disorders and oral apraxia in the case of motor aphasia.)

If these elementary conditions of unbiassed classification are taken into account it should be possible, to some extent, to reach general agreement, comparatively independent of the various theoretical stand­points. At least, we should be able to avoid - or reduce to a minimum - the mutual misinterpretations which constantly occur among apha­siologists of different schools. Many seemingly fundamental differen­ces of opinion are due to different starting points caused by differences in classification. In fact, the lack of a common and reliable classifica­tion is widely responsible for the chaos of contemporary aphasiology.

Purely as an example which, in my opinion, meets these require­ments of a practicable and reliable classification, I would like to men­tion briefly our own system of classification.

The theoretical background of our classification is the idea that the term "aphasia" should be limited to troubles which primarily and immediately concern language as a specific human property. Such troubles are revealed by erroneous interpretation of a verbal message (on the receptive side), and, on the expressive side, by faulty use of language as demonstrated, for instance, by the appearance of verbal paraphasias.

Adopting the notion of aphasia in this restricted sense, we must acknowledge quite a number of non-linguistic disorders which only secondarily affect certain aspects of the complex processes of speech.

30 E. Bay

Such non-linguistic disorders include, for example, dysarthria as a primary motor disturbance of the articulatory muscles impairing speech production; or a hearing defect which would hamper receptive per­formances. Euphoric lack of self-criticism and lack of ideas are ge­neral mental disorders which may produce specific changes in an aphasiac's behavior. Other examples of this type would be visual defects in cases of alexia.

All these non-linguistic factors can be defined exactly and unequi­vocally, and it is, therefore, not difficult to state with precision whether they are present or not. And with appropriate methods of examination it is even possible to estimate, with more or less exacti­tude, the degree of the respective disturbance.

Also regarding aphasia in the stricter sense there is no problem about ascertaining its presence or absence, and estimating the degree of an aphasic disorder. However, we were not able to find sharply differing types of aphasia which could be distinguished by clear and unequivocal properties. Therefore, to avoid arbitrariness and subsequent confusion, we prefer to refrain from further differentia­tion within the range of aphasia. With out present state of know­ledge - or rather ignorance - we have the impression that this is a more exact and a more scientific approach, than to introduce sub­groups which are biassed and capriciously defined. These must ne­cessarily increase confusion while they contribute nothing to our real knowledge, except their preposterous names.

Our scheme of classification, therefore, is confined to the dia­gnosis of aphasia, accompanied or not by dysarthria, euphoria, lack of self-criticism etc., of major or minor degree.

The essential advantage of this system of classification is the fact that the presence or absence of every item of the system can be stated with a clear "yes" or "no," irrespective of any theoretical im­plications. This contrasts with the reasoning on ambiguous hypotheti­cal grounds upon which the differentiating procedures of the classical system were based. So, for instance, a given case might be classified in the usual manner as "alexia without 'essential' aphasia and with­out such visual defects as could 'explain' the reading troubles." In our scheme the same case would appear as "mild aphasia accom­panied by visual defects and reading disability." How far the diffi­culties in reading depend upon aphasia, on visual defects, on a com­bination of both of them, or upon an independent alexia, is a problem

The classification of disorders of speech 31

which can be solved only by further investigations, and not by prejudiced guess-work.

I do not put forward our classification as the only possible one, but rather as an example to demonstrate the essential principles of a reliable and generally acceptable schema. I would insist that for such a classification it is necessary to take into full consideration, and to differentiate clearly from aphasia, the non-linguistic disorders of speech-activity. I would, however, also be prepared to accept a fur­ther differentiation of aphasia in its restricted sense, were there subgroups which could be unequivocally defined.

Prof. Dr. E. Bay, Moorenstrasse 84, Dusseldorf, Deutschland.