In order to arrive at the diagnosis of the nature of the lesion we must consider the family history, trace out predispositions, study the various causes of disease to which the patient has been exposed, and by a thorough examination of the various functions and the objective condition of the patient ascertain what pathological processes are active in him. Often the clue to the diagnosis is found in signs afforded by non-nervous organs, as nervous syphilis by nodes and cutaneous cicatrices, cerebral hemorrhage by renal disease and increased arterial tension, cerebral tuberculosis by pulmonary lesions, etc.
A purely empirical form of knowledge of some utility in proving the pathological diagnosis is that of the relative frequency of certain lesions in the two sexes, at different ages, in various professions, etc.—a statistical knowledge which is to be applied deductively to the case under study.
Considerable uncertainty sometimes remains even after the most careful analysis of a case, and often, after stating the first and second diagnoses quite positively, scientific caution and due regard for truth compel us to state the third diagnosis in alternative propositions or as a diagnosis of probability, to be finally settled by the appearance of new symptoms, or in some rare cases only by a post-mortem examination.
II. The Diagnosis of Functional Nervous Affections (Neuroses and Psychoses).
In some diseases of this class—as, for example, epilepsy—it is desirable to make the triple diagnosis as stated supra, but usually the two problems to be solved are—What is the symptom-group? and what is the pathology of the affection? The question of localization is less important and less easy of solution, as the symptoms are more usually generalized, often vague, and sometimes purely subjective.
1. The first diagnosis is to be made in the same manner as already stated, but besides, in many cases, a close psychological analysis is required to ascertain the emotional and mental state of the patient. Not only is this indispensable in cases of insanity, but it is often of great utility in other conditions, as hysteria, hypochondriasis, and simulation. In the course of this study we are frequently brought face to face with a most difficult problem—viz. the correct estimation of the degree of pain experienced by a patient. Is it a quasi-objective, correctly-portrayed sensation? is it magnified by abnormal sensitiveness or by true exaggeration? or is it simulated for a purpose? These questions demand the greatest freedom from prejudice and most delicate tact for their solution, and occasionally the most experienced physician is deceived. More especially are caution and scientific doubt to be exercised when this symptom (pain) stands alone or nearly so, as in some medico-legal cases and in certain hypochondriacal states where self-delusion seems to constitute the only real disease.
2. The diagnosis of the pathological nature of the functional disturbance (functional lesion) is to be made only by an exhaustive study of the patient's personal and family history and of his general condition. The following are the principal lines of inquiry to be followed:
(a) As to hereditary predisposition: direct or indirect inheritance of neurotic tendencies, of psychic peculiarities, and as to the presence of the various psychic and physical signs grouped under the term psychic degeneration.