Differential Diagnosis in Internal Medicine

1.1Elements of the Differential Diagnosis

Disease and Differential Diagnosis

Practical Procedure for Establishing a Diagnosis

Correct Evaluation of Evident Findings and the Differential Diagnosis

How to Handle Errors in the Medical Field

Factors That Can Lead to False Diagnoses

Physician-specific Problems

Patient-specific Problems

1.2 Factors That Can Influence the Differential Diagnostic Thought Process

Prevalence of Diseases

Age

Gender

Lifestyle

Eating Habits

Season, Time of Day, and Weather

Geographic Distribution

Ethnic Groups

Profession and Leisure

Precluding or Promoting Diseases

1.3 Differential Diagnosis by Groups of Diseases

Degenerative Conditions

Infectious Diseases

Immune Mediated Diseases

Tumors

Metabolic Diseases

Dysfunction of the Endocrine System

Mental Disorders

Hereditary Diseases

Chromosome Anomalies

Simple Mendelian Genetics

Multifactorial Heredity

Allergies

Intoxications

1.1  Elements of the Differential Diagnosis

Disease and Differential Diagnosis

Decision-making on the Basis of Diagnosis. The physician endeavors to organize the subjective complaints and the objective findings of a patient in order to receive further indications to proceed (d?a?????s??: to examine, to carefully consider, to differentiate, to become distinctively acquainted with, to decide). This approach is frequently chosen because a diagnosis in the conventional sense is not always easy to make, as more than one diagnosis can often be possible at the same time. Therefore, an important first step is to create a list of problems with a detailed description.

Dynamics of Reaching a Diagnosis. The diagnosis is of utmost importance not only for the prognosis but also for the introduction of an appropriate therapy. An established diagnosis always needs to be reassessed. Secondary diseases, complications, and side-effects can supervene. Each diagnosis continues to be a differential diagnosis, since the particular symptoms, even during the course of a disease, have to be continually reevaluated, carefully considered, and differentiated. For a proper evaluation of the symptoms and risk factors, knowledge of their clinical meaning is crucial. Consequently, the purpose of differential diagnosis is to point out what diseases can occur, when specific symptoms appear, and what risk factors with the utmost probability accompany specific diseases. In most cases, there are numerous possibilities and additional factors (frequency of disease, patient's age, secondary symptoms) that have to be taken into account. Exclusively listing all the possibilities would not be beneficial.

Typical clinical pictures are not as frequent because of early detection of many diseases and appropriate therapies. The typical course of diseases has also become less frequent. In addition, one has to allow for biological variability.

Etiology and Course. Different aspects must be considered in order to judge a clinical picture. The study of the causes of disease, the etiology, has eclipsed the approach of nosology even in terms of therapeutic measures. Therefore the nosological entity "pneumonia" only describes a complexity of symptoms and starting point for the purpose of etiological differentiation (e. g., pneumococci, mycoplasma, chlamydiae, legionellae, viruses). Depending on the immunity and age of a patient, the course of the disease can be different even with identical pathogens, e. g., drastically different complication rates. Another example is that specific microorganisms may lead to so-called opportunistic infections in immunosuppressed patients, whereas in immunocompetent patients they do not. Where a patient is in fact examined (private practice, outpatient clinic, emergency department) also plays a significant role for the differential diagnosis.

Pathogenesis. The knowledge of pathogenesis must suffice in many cases in order to define a clinical picture. Pathogenic differentiation of various forms of hypertension is necessary for therapeutic and prognostic reasons. Despite research in etiology and pathophysiology we often proceed in a descriptive manner.

Criteria, Scores, Algorithms. Diagnoses as conceptual entities and bases for therapeutic measures are partially replaced by a system of criteria, which automatically leads to the next diagnostic or therapeutic step. This procedure is absolutely essential in specific situations, such as in emergency and intensive care medicine. Therefore, apnea requires immediate artificial respiration independent from etiology and pathogenesis. The identification of apnea is not a diagnosis in the narrower sense, but a state that calls for a certain therapeutic action.

Triage Decisions, Emergency Situations. Most triage decisions are not based on a definite diagnosis. Experienced general practitioners make split-second judgements based on posture, gait, facial expression, expression of the eyes, eye contact, circumstances including attire and accompanying persons, calm or uneasy appearance, perspiration, facial color, as well as breathing, and any changes in known patients. Medical split-second judgements are correct in more than 64% of cases (Tab. 1.1). The clinical initial evaluation incorporates the very first visual, auditive, olfactory, affective, and intuitive impressions.

Judgements based on an evaluation made in a few minutes are very often correct. However, they must also be reassessed and adjusted according to the dynamic of the disease.

The emergency evaluation plays an important role in the medical field. The evaluation of vital signs such as temperature, respiratory rate, blood pressure, and pulse is essential. It may be necessary to observe the patient for several hours in order to make the correct triage decision concerning hospitalization. The criteria for nonemergency situations are summarized in Tab. 1.2. Impaired consciousness and suicidal tendency are among high-risk criteria.

Verification of Diagnosis. Establishing an accurate diagnosis is usually an essential prerequisite for treatment of a patient. In order to continually reassess a diagnosis, the physician is obliged to maintain a self-critical attitude, e. g., in order to reexamine the effect of an adopted therapeutic regimen. This is especially important when increasingly "atypical" progression occurs or the chosen therapy is ineffective. Pattern recognition is essential to diagnostic reasoning.

Diagnosis and Individual Expression of Disease. The picture of a disease is one-sided and incomplete unless the symptoms are coupled with the ill person. Each person molds the disease and its expression by his or her individualism. A must for the physician is to respect the patient's experience in terms of perception of the disease. Specific perceptions can be the key to the diagnosis. Only when patients feel they are being understood can they be persuaded to go through stressful diagnostic processes ("shared decision-making"). Hence, the physician must comprehend the uniqueness of a patient's disease. The possibility that a patient called on him/her because of a so-called "hidden agenda" must also be borne in mind (see Chapter 2).

Diagnosis and Therapeutic Consequences. It is the job of the physician to take responsibility concerning the correct preliminary measures for each patient. The patient is entitled to interpret the disease in such a way that it correlates with personal circumstances. In view of multiple modern diagnostic methods and increasing healthcare costs, one is forced to carefully consider whether or not the effort in examining the patient and the patient's stressful situation is to be followed by therapeutic consequences.

Table 1.2   Criteria for a nonemergency situation are normal vital signs and absence of a high risk indicator

• Temperature 35-38.5°C
• Respiratory rate 12-20/min
• Blood pressure 90/60-160/110 mmHg
• Pulse rate 60-100/min

• Severe pain
• Chest or abdominal pain
• Younger than 16 years
• Unable to walk or arrival by ambulance
• Impaired consciousness
• Suicidal tedency

Individually Adapted Diagnosis. A differential diagnosis indicates only the components which are needed...