Diagnostic Principles and Applications
Robert B. Taylor, MD
This book is intended to make you a better clinician, as you learn some unfamiliar, perhaps even forgotten, pathways to important diagnostic destinations. If this book were a road map, it would be about the “blue highways”--the less-traveled roads, the ones that may become vital when the "red line" major highways don't get you where you need to go. Think about the observation by American laryngologist Chevalier Jackson cited above: When presented with a wheezing patient, an experienced clinician would consider asthma to top the list of diagnostic considerations. But, in certain clinical contexts, the astute clinician might also think of foreign body aspiration, Wegener granulomatosis, parasitic infection, or airway constriction by an aortic aneurysm. Considering these other possibilities is the first step in making the correct diagnosis.
Thus, this is not a typical, “comprehensive” differential diagnosis book, with long lists of diseases, most familiar to practicing clinicians, that might explain a symptom, sign, or abnormal laboratory finding. Instead I offer selected topics, the uncommon—and sometimes exasperatingly esoteric—disease causes we sometimes fail to consider. As an analogy, I offer the Lifeguard Paradox: If aspiring lifeguards were to spend the bulk of training time practicing what they will do most of the day at work, they would focus on learning to apply sunscreen to their own bodies. But in lifeguarding, unanticipated events happen, and the lifeguard must know how to handle them. In medicine, uncommon diseases and unlikely manifestations of common diseases occur with sometimes-surprising frequency, and we need to review them from time to time.
Of course, clinicians also encounter the some diseases—whether everyday or rare--that we especially do not want to overlook, such as toxic megacolon and testicular torsion; when one of these appears in the coming pages it is tagged as a must-not-miss diagnosis.
In this book, the emphasis is on the enlightened uses of traditional diagnostic tools—clinical history, physical examination, and basic laboratory tests and imaging. The more esoteric investigative methods—PET scans and genetic testing--seem to evolve constantly, and are best studied in journal and web-based sources that are more timely than books. Because the content of this book is selective, rather than attempting to be all-inclusive, I have tilted my choices toward identification of high-impact diseases. And also because this is a diagnosis book, I have included information about therapy only when I believed it would enrich the discussion or when I wanted to emphasize the urgency of reaching a timely, precise diagnostic end-point.
What will you find in this book? I have included the following categories of diagnostic facts:
Classical diagnostic pearls: For example, the patient with acute pericarditis often leans forward to relieve the anterior chest pain.
Red flag symptoms and signs of serious illness: A salty taste when kissing an infant may represent the first clue to a diagnosis of cystic fibrosis.
Counterintuitive clinical manifestations: The patient with gout may have a normal or low serum uric acid level during the acute attack; and nocturnal back pain has, in fact, not been found to be a useful indicator for serious spinal pathology.
Bellwether signs and symptoms allowing an occasional early diagnosis: Abdominal distension is a common early manifestation of ovarian cancer; and patients with gastric cancer sometimes lose their appetite for meat early in the course of the disease.
Curious clinical manifestations that may point to specific diagnoses: Here I think of the aquagenic pruritus of polycythemia vera, with itching that is aggravated by a hot shower. And the cutaneous “wake sign,” skin lesions resembling the wake left by a moving ship, has been described as seen only with scabies.
Who needs this book? As medicine has become increasingly specialized, medical books have become correspondingly limited in their scope. This book, on the other hand, casts a very wide net, presenting diagnostic facts related to all ages and body systems. Thus, intended readers include medical students, residents, and practicing physicians, nurse practitioners, physician assistants, nurses and, in fact, anyone involved in making diagnostic observations and decisions.
Do YOU need this book? Let’s see. If you see real, live patients in any specialty setting and cannot answer the following are five questions, I suggest that you put Diagnostic Principles and Applications high on your reading list:
1. What are the three characteristics of the scenario in which a diagnosis of breast cancer is often missed?
2. Of all the sites of possible lymphadenopathy, which is the most worrisome?
3. Low back pain that improves with forward flexion of the spine suggests what diagnosis?
4. Hyponatremia may be the clue to what psychiatric disorder?
5. Can you describe the Au-Henkind test for acute iritis, the Wartenberg sign in ulnar nerve palsy, and the Tullio phenomenon as a clue to the cause of vertigo?
What are key features of this book? Medical education and clinical experience are remarkably capricious. A newly minted medical graduate may never have seen a patient with Guillain-Barré syndrome or osteomyelitis of the spine. Even the experienced practitioner may never have encountered anyone complaining of pathologically excessive yawning or a patient with suspected cerebrospinal fluid rhinorrhea. Owing to the variability in individual training and experience, each reader will be well acquainted with some of the entities described in this book, considering what I present to be well known and wondering why I included them at all. Others will find this same information to be new knowledge. For the most part, I have attempted to select facts not generally covered in basic physical examination courses or textbooks.
Traditional diagnosis books are organized by symptoms and signs—hemoptysis, chest pain or bullous eruption of the skin—in contrast to disease-oriented reference books, which are organized by names of various clinical entities: lung cancer, myocardial infarction, or pemphigus. In this book, I present information under both types of headings, manifestations and diseases. When questions arose, I listed items under the body organ or system in which manifestations are most likely to occur. For example, consider the clue that the patient with herpes zoster who develops a vesicle near the tip of the nose is at risk of developing herpes zoster ophthalmicus; this pearl is presented in Chapter 5 (The Ear, Nose, and Throat) rather than Chapter 4 (The Eye).
To save space, and with apologies to all the often-anonymous “et al” co-authors of the world, I have used a shorthand reference style, citing the first author only, plus article title, journal, year, volume and initial page number. Using an abbreviated reference style allows more pages for facts, and still provides enough information to find the article on PubMed, BioMedLib, or Google Scholar. Also, readers will find reference citations listed immediately following the stated fact and commentary, rather than at the end of the chapter; in my own reading I find this placement of references to be especially helpful. In the appendix, I have included a list of a glossary of statistical terms used in the book.
This book is literature-based, by which I mean that all facts in this book are found somewhere in the medical literature. Not all assertions, however, are classically evidence-based. We just don’t know with precision (or, at least, I could not locate) the sensitivity or specificity of uncommonly occurring clinical manifestations, such as upbeating nystagmus sometimes observed in Wernicke encephalopathy, or the positive predictive value of some uncommon observations, such ¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬the “red ear syndrome” that has occurred in some patients with migraine. Some phenomena presented, such as yellow vision with digitalis intoxication, represent examples of often-repeated clinical lore, validated by repeated observations of experienced clinicians, and are included because they seem to be have weathered the test of time, supported by a few case reports. But most of what is presented here, such as the positive correlation of a high pulse pressure and white coat hypertension, has been subjected to statistical analysis and peer review. I recognize that some of what I describe is controversial and that future clinical studies may lead us to reconsider what we think is true and wise today. I urge the reader to use this book as a series of prompts, and then consult the current literature before making clinical decisions if in unfamiliar territory.
In my research for this book, I found that a number of my reference citations for physical findings and diagnostic maneuvers--such as the Lisker tibial tap sign for deep vein thrombophlebitis of the lower extremity, discussed in Chapter 6--are found in literature that some may call "dated." Today, teaching indicator symptoms and physical biomarkers of disease seems to be out of style in medical school, and as Verghese writes, “Because the echocardiogram, magnetic resonance imaging, and computed tomographic can precisely characterize anatomy, the physical exam is too often viewed as redundant.”  I hold that so-called "old-fashioned" historical clues and physical signs are not only part of our medical heritage; their recognition can often spell the difference between prompt identification of disease versus an expensive, time-consuming journey through the clinical laboratory and diagnostic imaging suite. In fact, with the inconsistent quality of medical school teaching regarding the physical examination and the rising costs of high-tech health care, I think this book is needed more than ever.
How should you use this book? This is not a classical course text to be studied in a classroom setting. Nor is it a clinical reference book, intended to be “searched,” but not really “read.” This is a “topical” book, presenting a somewhat eclectic collection of facts that someday may prove useful in specific puzzling situations. Hence, the book should be read, cover-to-cover. Put it at your bedside; take it to the beach; enjoy it on a plane trip. The goal is both to learn diagnostic principles and applications today, and to imprint them deep in your memory for future reference. I continue to like my metaphor of “Post-It” notes used to describe my book: Essential Medical Facts Every Clinician Should Know.  What you read today may not be clinically pertinent for months or years, but when the time comes, the information is there, “posted” in memory. Then, just to confirm your recollection, you can find it here again using the index provided or perhaps check out the original report on-line.
In addition to my “read, post it, recollect, and confirm” approach, the book’s index will be a good place to look when faced with a head-scratching, seemingly unsolvable diagnostic puzzle. Use the index to locate the answers to the five questions posed above.
It is axiomatic that the most common diseases occur most commonly. What clinician has not heard the axiom that when you hear hoof-beats, expect to hear horses, not zebras? But it is also true that we all encounter the uncommon entity occasionally, perhaps when we least expect to do so. Knowing the contents of this book can help you recognize the unlikely disease manifestation of a “horse” disorder or spot the “zebra” diagnosis when it presents itself in the middle of a busy office session or on an exam question.
Finally, this book is intended to be easy to read, with just enough statistical details to support assertions, without becoming excessively burdened with methodologic minutiae. I have attempted to enrich your knowledge of our heritage by including a few historical anecdotes. And most of all, I have done my best to make this book clinically useful, as the title says:
To prevent medical errors
Pass board examinations,
Provide informed patient care
1. Jackson C. A new diagnostic sign of foreign body in trachea of bronchi, the “asthmatoid wheeze.” Am J Med Sci. 1918;156:626.
2. Verghese A. Culture shock: patient as icon, icon as patient. N Engl J Med. 2008;359:2748.
3. Taylor R. Essential clinical facts every clinician should know. New York: Springer; 2011.
Robert B. Taylor, MD
Oregon Health & Science University