INTRODUCTION TO DIFFERENTIAL DIAGNOSIS AND DIAGNOSIS OF COMMON PROBLEMS
Diseases are defined by a pattern of symptoms the patient reports, signs observed during physical examination, and diagnostic testing. Deter- mining the differential diagnosis is the process of distinguishing one dis- ease from another that presents with similar symptoms. With the chief complaint established, information is gathered through the history and physical examination. When the patient presents with a chief complaint, such as cough, the provider considers the most common diseases that present with cough, forming a working differential diagnosis list. The provider analyzes the data obtained, eliminates some diseases, and nar- rows down the differential diagnosis. At times, further diagnostic testing is needed to make the final diagnosis. The construction of a differential diagnosis is essential in making an accurate diagnosis.
PATIENT HISTORY
Identification/Chief Complaint The first piece of information obtained is the chief complaint or the patient’s reason for seeking medical attention. This statement gives the provider a general idea of possible diagnoses. For example, “a healthy 16- year-old boy presents with a nonproductive cough he’s had for 3 days.” Subjective The most common etiology of the disease is in the ears, nose, throat, and respiratory system. With this in mind, the provider asks the patients a se- ries of open-ended questions to gather data related to the presenting prob- lem. These questions form the basis of the symptom analysis: •Onset •Location/radiation •Duration/timing •Character •Associated symptoms •Aggravating or triggering factors •Alleviating factors •Effects on daily life Once a general history is obtained, the provider moves on to obtain more details through a directed history. Patients may not offer pertinent symp- toms unless prompted. These questions are focused on the diagnostic possibilities related to the presenting problem. For example, a patient who presents with chest pain may not recall that the pain is much better when he or she leans forward, indicating possible pericarditis. Once questions regarding the symptom are completed, the provider moves on to obtain data regarding the patient’s general health status, and relevant past medical, family, and social history. The patient’s past med- ical history and family history outline risk factors for diseases. The social history may reveal occupational exposures or habits that influence the presence of diseases, such as heart and lung disease from smoking, or liver disease from alcohol or drug use.
PHYSICAL EXAMINATION
The physical examination starts when you walk into the room and observe the patient’s general appearance. Visual clues include facial expression, mood, stress level, hygiene, skin color, and breathing pattern. Although they may seem trivial, the assessment of vital signs is critical, and their accuracy is imperative. The presence of fever, tachycardia, or low blood pressure is cause for concern and alerts the provider that the patient may have a serious disease. Unlike the patient who comes in for a comprehensive physical examination, the patient who presents with a symptom requires a focused physical examination. The examination is directed by the chief complaint and history. For example, a 16-year-old with a recent cough requires examination of the ears, eyes, nose, throat, neck (for lymphadenopathy), heart, lungs, and abdomen (for an enlarged liver or spleen). Attention is given to the skin to look for cyanosis, the nails for clubbing, and the vascular system for edema. Neurologic examination is limited to mental status, and other parts of the examination are not relevant. The physical examination provides positive and negative findings, and may provide the diagnosis without the need for further testing. For exam- ple, if the examination of a patient who reports a painful skin rash yields findings of a cluster of vesicles on an erythematous base following a dermatome, this is a positive physical finding confirming a clinical diagnosis of herpes zoster. On the other hand, the lack of a rash would be a negative physical finding and further exploration would be needed. The physical examination may also reveal unsuspected findings, or may be completely normal despite the presence of disease.
DIFFERENTIAL DIAGNOSIS
Once the chief complaint, history, and physical examination are established, a list of possible diseases is formed ranking the most common diagnoses and the most serious or “not to miss” diagnoses. The axiom that common diseases present commonly and uncommon diseases are uncommon cannot be overstressed. Keeping an open mind, and explor- ing all possibilities, is important. Premature closure or discarding a diagnosis too early may result in diagnostic error. The depth of one’s differ- ential diagnosis is determined by the breadth of knowledge of the provider. A disease cannot be diagnosed and treated unless it is known to the provider. This can be a challenge for the novice who is faced with a mountain of information to learn about thousands of diseases. It results in a chronic sense of dissatisfaction with one’s knowledge base, and can be a source of great fear and frustration. However, it serves to stimulate exploration and learning, and with experience and guidance, knowledge grows. The novice will find that a solid reference enables him or her to master the task of differential diagnosis as his or her clinical experience matures.
DIAGNOSTIC TESTING
When the diagnosis cannot be made on history and physical data alone, diagnostic testing is the next step in determining the correct diagnosis. Diagnostic testing should be done only if necessary to yield an impact on the diagnosis, and ultimate treatment of the problem. Ordering unnecessary tests is enormously expensive. When possible, order basic tests to screen for disease, and if the diagnosis remains unclear, move on to more elaborate testing. Consider the sensitivity and specificity of a test as well. “Sensitivity” is the proportion of patients with the diagnosis who will test positive. “Specificity” is the proportion of patients without the diagnosis who will test negative. If the diagnosis is not defined by the history, physical examination, and diagnostic testing, the provider then needs to reevaluate the patient over time, reformulating new diagnostic possibilities as new signs or symptoms arise.
STEPS TO WRITING A DIFFERENTIAL DIAGNOSIS
Knowledge of how to write a medical diagnosis comprises several critical steps. 1.Obtain the patient’s chief complaint, such as “cough for 2 weeks” and list three common problems that present with that symptom. For example, acute cough is most likely viral bronchitis, pneumonia, or viral rhinosinusitis with postnasal drip. 2.Obtain a detailed history as outlined previously. Make a list of the pa- tient’s symptoms and pertinent risk factors. Note the pertinent posi- tive and negative associated symptoms. For example, a patient with a cough who has a high fever and shortness of breath (positives) likely has pneumonia. A patient who has a cough without a high fever or shortness of breath (negatives) may have viral bronchitis. Based on the information from your history, direct your physical examination to look for significant signs of illness. For example, is there sinus tender- ness? Is there a postnasal drip in the posterior pharynx? Are there wheezes or crackles present? 3.Review your differential diagnosis list of possible diagnoses based on the history and physical examination. Determine whether you need additional diagnostic testing based on your findings. For example, a patient with a fever of 102°F, heart rate of 120, and respiratory rate of 30 with diminished breath sounds in the right lower lobe and crackles will benefit from a chest x-ray to confirm the presence or absence of pneumonia. A complete blood count will identify whether there is a significant leukocytosis or elevated white blood cell count. A basic metabolic panel will ascertain whether there is an electrolyte imbal- ance or dehydration. 4.Establish a clear determination that shows why this particular diagnosis is accurate for the patient. Review your rationale for why you chose this diagnosis as opposed to others on your list of possibilities. Keep an open mind as you review your facts for any other diagnostic possi- bilities you may have missed, including a life-threatening illness. 5.Develop a treatment plan, including diagnostic testing, pharmacologic agents, patient education, and follow-up. If your diagnosis remains un- clear, consider appropriate referral for further evaluation.
SUMMARY
This book is written to help the reader learn the process of formulating a differential diagnosis using the skills of gathering appropriate data from the history, physical examination, and relevant diagnostic testing. Each chapter is interspersed with cases describing an initial chief complaint, history, and physical examination. Tables outlining the common diagnosis with cardinal signs and symptoms as well as diagnostic testing are provided for the reader’s review. Clinical diagnostic reasoning for the final diagnosis is outlined. The approach is to give pertinent information as well as demonstrate the process of clinical reasoning. It is well known that the process of differential diagnosis takes years to master. It is especially challenging for new students learning the complexities of diagnosis. It is our hope that this book will help you start your journey with the tools to make this learning process interesting and relevant.