In any doctor-patient interaction, both parties have one goal in mind: to minimize the patient's illness. To do so, the doctor must determine what the problem is and manage it accordingly. This requires a thought process to interpret information from the patient and evaluate the possible causes for the illness.
Many people may wonder how this works. What exactly are doctors thinking when they see a patient? The following is an overview of clinical diagnosis, accompanied by a simplified example to illustrate the process.
Patient History
When a patient is ill, he or she reports the primary symptom to a doctor. Because every symptom has multiple causes, the doctor interviews the patient to narrow the possibilities. Initial questions for the patient usually pertain to details of the symptom (e.g., timing, location in the body, and aggravating factors) and any associated symptoms. Other questions may explore past medical conditions (past medical history), conditions among biological family members (family history), and habits related to work and leisure (social history), all of which identify risk factors for certain conditions.
Example: Suppose Mr. X, a 58-year-old male patient, sees Dr. A in the clinic because of shortness of breath (dyspnea). Through interviewing, Dr. A learns that the dyspnea mainly occurs with walking, which has never happened before. Mr. X has never smoked and does not have any known lung disease, but he does not get regular screening tests. Based on this information, Dr. A considers a wide variety of possible diagnoses (differential diagnosis), including but not limited to congestive heart failure, aortic valve regurgitation, and anemia.
Physical Examination
Besides symptoms the patient can identify, diseases can also produce abnormalities that a patient cannot sense but a physician can detect on physical examination. A physical examination consists of looking at (inspection), feeling (palpation), and listening to (auscultation) parts of the body from head to toe. Certain portions of the physical exam involve additional special maneuvers, such as the use of a reflex hammer. The purpose of the physical exam is to obtain additional clinical information that could further narrow the differential diagnosis.
Example: Dr. A listens to Mr. X's chest and finds that the lungs are clear and the heart has no murmurs or other abnormal sounds. However, Mr. X looks pale under the lower eyelids. The rest of the exam is unremarkable. At this point, Dr. A is more worried about anemia and less concerned about aortic regurgitation, but he is careful not to rule out too many possibilities at once.
Diagnostic Testing
If the probability of certain diagnoses is halfway between likely and unlikely, the doctor can request certain tests on the patient, such as blood tests, pathological analyses of biopsy samples, and imaging studies. The results of such diagnostic tests increase or decrease the likelihood of the diagnoses in question. Like the history and physical exam, diagnostic testing provides new information that further narrows the differential diagnosis.
Example: Concerned about anemia, Dr. A orders a complete blood count for Mr. X. The doctor also requests a colonoscopy since colon cancer can cause unnoticed rectal bleeding. Just to be certain, Dr. A orders a few other tests, including a chest x-ray. Results show that Mr. X's hemoglobin level is much lower than normal and that Mr. X's colon has a malignant tumor.
Assessment and Plan
Based on the available clinical information, the doctor summarizes the most likely diagnosis and its rationale. The doctor then formulates a plan that involves further diagnostic testing and/or treatment depending on the certainty of the diagnosis.
Example: Dr. A concludes that Mr. X's dyspnea is secondary to anemia, which in turn is the result of bleeding from colon cancer. The doctor will order a whole-body imaging study to see if the colon cancer has spread (metastasized). Dr. A will also refer the patient to a surgeon for possible colectomy and to an oncologist who will determine the necessity of chemotherapy and/or radiation therapy.
Final Words
Every medical condition has its own symptoms and signs, which overlap with those of other conditions. To explain any clinical manifestation, a doctor works backward from the symptoms and signs to the possible conditions. The process is very methodical and detailed, requiring cooperation between the doctor and the patient for best results.
Reference
Bickley, Lynn S. and Szilagyi, Peter G. Bates' Guide to Physical Examination and History Taking. 8th ed. Philadelphia: Lippincott Williams & Wilkins, 2003.
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