1 What is pathology? James C. E. Underwood History of pathology 4 Making diagnoses 9 Morbid anatomy 4 Diagnostic pathology 9 Microscopic and cellular pathology 4 Autopsies 9 Molecular pathology 5 Pathology, patients and populations 9 Cellular and molecular alterations in disease 5 Causes and agents of disease 9 Scope of pathology 5 The health of a nation 9 Clinical pathology 5 Preventing disability and premature death 9 Techniques of pathology 5 Pathology and personalised medicine 10 Learning pathology 7 Disease mechanisms 7 Systematic pathology 7 Building knowledge and understanding 8 Pathology in the problem-oriented integrated medical curriculum 8 3 PatHOLOGY, PatIENTS AND POPULatIONS 1 Keywords disease diagnosis pathology history 3.e1 1 WHat IS patHOLOGY? Of all the clinical disciplines, pathology is the one that most Table 1.1 Historical relationship between the hypothetic directly reflects the demystification of the human body that has causes of disease and the dependence on techniques for made medicine so effective and so humane. It expresses the truth their elucidation underpinning scientific medicine, the inhuman truth of the human body, and disperses the mist of evasion that characterises folk Techniques medicine and everyday thinking about sickness and health. Hypothetical supporting causal From: Hippocratic Oaths by Raymond Tallis cause of disease hypothesis Period Animism None Primitive, although Pathology is the scientific study of disease. Pathology the ideas persist in comprises scientific knowledge and diagnostic methods some cultures essential, first, for understanding diseases and their causes and, second, for their effective prevention and treatment. Magic None Primitive, although Pathology embraces the functional and structural changes the ideas persist in in disease, from the molecular level to the effects on the some cultures individual patient, and is continually developing as new research illuminates our knowledge of disease. Humours (excess Early autopsies and c. 500 BC to c. AD The ultimate goal of pathology is the identification of the or deficiency) clinical observations 1500 causes and mechanisms of disease leading to successful therapy Spontaneous Analogies with Before AD 1800 and disease prevention. Without pathology, the practice of generation decomposing matter medicine would still rely on myths and folklore, and conse- (abiogenesis) quently be ineffective. Environmental • Modern autopsy 1850 to present HISTORY OF PATHOLOGY • Cellular pathology (e.g. microscopy) Evolving concepts about the causes and nature of human • Toxicology disease reflect prevailing explanations for all worldly events • Microbiology and also the techniques available for their investigation (Table • Epidemiology 1.1). Thus the early dominance of animism, for example in Genetic Molecular pathology 20th century to the philosophies of Plato (424–348 BC) and Pythagoras (c. (e.g. DNA analysis) present 580–c. 500 BC), led to the belief that disease represented the and clinical observa- adverse effects of immaterial or supernatural forces, often tions on inherited as punishment for wrongdoing. Treatments were often brutal defects and ineffective. When many symptoms, signs and postmortem findings were first believed to have natural explanations, the underlying disease was postulated to be due to an imbalance (‘isono- by Matthew Baillie (1761–1823), Carl von Rokitansky mia’) of the four humours — phlegm, black bile, yellow (1804–1878) and Ludwig Aschoff (1866–1942). They meticu- bile and blood — as proposed by Empedocles (490–430 BC) lously performed and documented many thousands of and Hippocrates (c. 460–370 BC). These concepts are now autopsies and, crucially, correlated their findings with the obsolete. clinical signs and symptoms of the patients and with the Galen (129–c. 200) built on Hippocrates’ naturalistic ideas natural history of numerous diseases. about disease by giving them an anatomic and physiological basis. However, it was probably Ibn Sina (980–1037) — Microscopic and cellular pathology commonly known as Avicenna — who, by his Canon of Medicine, pioneered advances in medicine through scientific Pathology, and indeed medicine as a whole, was revolutionised discovery by observation, experimentation and clinical trials. by the application of microscopy to the study of diseased tissues from about 1800. Previously, it was commonly believed Morbid anatomy that tissue alterations in disease resulted from a process of spontaneous generation; that is, by metamorphosis independ- Some of the greatest advances in our understanding of disease ent of any external cause or other influence. Today, this notion emerged from internal examination of the body after death. seems ridiculous, but 200 years ago nothing was known of Autopsies (necropsies or postmortem examinations) have bacteria, viruses, ionising radiation, carcinogenic chemicals, been performed since about 300 BC and have helped to clarify and so on. Louis Pasteur’s (1822–1895) demonstration that the nature of many diseases. As these examinations were microorganisms in the environment could contaminate and confined initially to the gross (rather than microscopic) impair the quality of wine was a major advance in our percep- examination of the organs, this period is regarded as the era tion of the environment and our knowledge that pathogens of morbid anatomy. A notable landmark was the publication within it, invisible to the naked eye, cause disease. in 1761 of De Sedibus et Causis Morborum per Anatomem Indagatis Rudolf Virchow (1821–1902), a German physician and by Giovanni Morgagni (1682–1771). During the 18th and pathologist and an ardent advocate of the microscope, rec- 19th centuries in Europe, medical science was further advanced ognised that cells were the smallest viable constituent units 4 TECHNIQUES OF PATHOLOGY 1 of the body. Building on the work of Theodor Schwann haematology: the study of disorders of the cellular and (1810–1882) he formulated a new and lasting set of ideas coagulable components of blood about disease — cellular pathology. The light microscope microbiology: the study of infectious diseases and the organ- enabled diseased tissues to be viewed at a cellular level. His isms responsible for them observations, extended further by electron microscopy, have immunology: the study of the specific defence mechanisms had a profound and enduring influence. But Virchow’s cell of the body pathology theory is neither complete nor immutable; advances chemical pathology: the study and diagnosis of disease from in biochemistry have revolutionised our understanding of the chemical changes in tissues and fluids many diseases at a molecular level. genetics: the study of abnormal chromosomes and genes toxicology: the study of the effects of known or suspected Molecular pathology poisons forensic pathology: the use of pathology for legal purposes The impact of molecular pathology is exemplified by advances (e.g. investigation of death in suspicious circumstances). in our knowledge of the biochemical basis of congenital disorders and cancer. Techniques with relatively simple These subdivisions are more important professionally principles (less easy in practice) reveal the change of a single (because each requires its own team of trained specialists) nucleotide in genomic DNA resulting in the synthesis of the than educationally at the undergraduate level. Pathology must defective gene product that is the fundamental lesion in a be taught and learnt in an integrated manner, for the body particular disease (Ch. 3). and diseases make no distinction between these professional subdivisions. This book, therefore adopts a multidisciplinary Cellular and molecular alterations in disease approach to pathology. In the systematic section (Part 3), the normal structure and function of each organ is summarised, Modern scientific methods have resulted in a clearer under- the pathological basis for clinical signs and symptoms is standing of the ways in which diseases result from disturbed described, and the clinical implications of each disease are normal cellular and molecular mechanisms (Table 1.2). emphasised. SCOPE OF PATHOLOGY TECHNIQUES OF PATHOLOGY Scientific knowledge about human diseases is derived from Our growing knowledge of the causes and mechanisms observations on patients or, by analogy, from experimental of disease has emerged from advances in science and studies on animals, cell cultures and computer simulations. technology. The greatest contribution comes from the detailed study of tissue and body fluids from patients. Pathology also has a Gross pathology key role in translational research by facilitating the transfer of knowledge derived from laboratory investigations into Before microscopy was applied to medical problems (c. 1800), clinical practice. observations were limited to those made with the naked eye, and thus was accumulated much of our knowledge of the Clinical pathology morbid anatomy of disease. Gross or macroscopic pathology is the modern nomenclature for this approach to the study Clinical medicine involves a longitudinal approach to a of disease and, especially in the autopsy, is still important. patient’s illness — the patient’s history, the examination and The gross pathology of some diseases is so characteristic investigation, the diagnosis, the treatment and follow-up. that, when interpreted by an experienced pathologist, a fairly Clinical pathology is more concerned with a cross-sectional confident diagnosis can be given before further