What is internal medicine?

Science and Profession

Internists, or practitioners of internal medicine, are skilled in the diagnosis and treatment of disease conditions that can occur virtually anywhere within the human body. They must be expert in human biology and anatomy and in pathophysiology (that is, the study of the processes that lead to disease conditions). By its nature, internal medicine embraces many other medical specialties, such as cardiology and gastroenterology. In fact, many internists become certified in related specialties.

The original model for the modern internist was Sir William Osler (1849–1919), a Canadian physician who practiced in the United States for much of his life. Osler was deeply beloved and respected for his compassion and humanity as well as his extraordinary skills in anatomy and diagnosis and in effecting cures for his patients. In his long career as physician and teacher of medicine, Osler formulated many of the guiding principles in the practice of internal medicine.

Knowledge of many scientific disciplines is required of internists. They must understand the physical and biological bases of disease. This involves knowledge of genetics, cellular biology, immunology, and the activities and nature of the various microorganisms that cause disease, such as bacteria, viruses, fungi, yeasts, and parasites.

Internists must understand the components and roles of each type of cell in the human body and know how the cell functions. Human cells are not simple entities, but complex miniature organisms with many activities going on simultaneously, particularly metabolic processes. Just as important, internists must understand what happens within and outside the cell in the disease process. For example, they must know how individual bacteria cause infection and how viruses invade cells, use them for their replication, and then destroy them. Internal medicine involves all the body’s organ systems and structures, such as the heart and circulatory system, the gastrointestinal system, the genitourinary system, the respiratory system, the skin, the brain, and the skeletal system.

Internists must also be able to examine patients and diagnose the presence or absence of disease. This process involves a wide variety of techniques and procedures. It usually begins with an introductory interview, followed by physical examination of the patient. Pain is the most common symptom of disease, and manifestation of it is investigated thoroughly.

Diagnostic and Treatment Techniques

Internists understand the intricate pathways of pain throughout the body and know that proper explanation of a pain will often lead directly or indirectly to a correct diagnosis of the underlying disorder. Much of the diagnostic skill of the internist, however, is in the understanding that pain may be ambiguous. Headache can point to the possibility of many disorders, ranging from sinusitis to severe pathologies within the brain. Pain in the chest can be caused by upper respiratory tract infection or heart disease. Pain in the limbs and/or joints may indicate physical trauma as a result of accidents or overexercising, or it may be attributable to arthritic or rheumatic disease or other causes. Abdominal pain can be present in literally dozens of different conditions. Similarly, back and neck pain can be caused simply by physical exertion or may point to a serious underlying disease.

Blood pressure and pulse are checked in the physical examination, and the doctor listens to heart and chest sounds through a stethoscope. The ears, mouth, and nose are examined. Body temperature is an important diagnostic consideration. Excess body heat or fever often accompanies infection and may also be present in other disease conditions. The doctor also checks for enlargement of lymph nodes and other signs that might suggest infection or other disorders.

Blood or urine samples are often taken for laboratory analysis. The internist will specify the tests he or she wants in the laboratory workup. These will include standard assays to give the internist a general picture of the patient’s health and may include special tests for individual functions that the doctor may suspect are impaired.

Changes in the function of different body systems can lead the physician through the process of diagnosis. For example, such symptoms as dizziness; fainting; numbness; vision, speech, or hearing disturbances; or coma may be caused by dysfunction of the nervous system or may point to heart disease or other disorder. Abnormalities in respiratory function have specific meaning to the internist and may lead to a diagnosis ranging from a common cold to a more serious respiratory disease or a disease of other organs, such as the heart. Alterations in the skin may indicate a dermatological disorder or may suggest some internal condition.

Sometimes, a diagnosis is easy to make: The presenting symptoms are obvious signs of a specific disease. Sometimes, a group of symptoms, called a syndrome, may be ambiguous and could be related to any of a number of conditions. If the exact nature of a disease or its cause is uncertain, the internist will conduct a differential diagnosis in which possible causes of the disease are investigated in order to eliminate those that are not candidates and to pinpoint the actual cause.

Internists treat a wide variety of disorders. Among the most significant are the infectious diseases. They must study the pathogenesis (from pathos, meaning “disease,” and genesis, meaning “origin” or “source”) of infectious diseases in order to know how to diagnose and treat them. Harmful bacteria cause disease in different ways, but all damage and destroy body cells and tissue. Some cause infection at the point where they enter the body, such as at the site of a wound, or in the respiratory tract when they are breathed into the body. Sometimes, bacteria are carried from their site of entry to other parts of the body, where they colonize and cause infection.

The range of bacterial infections is enormous, but one thing that they often have in common is inflammation. Inflammation is the beginning of the immune process by which the body defends itself against invading pathogens. It starts when the body recognizes that the invading organism is a foreign entity by detecting foreign antigens (substances on the surfaces of invading organisms such as bacteria and viruses). The body then releases certain white blood cells, called leukocytes, that are specific for producing antibodies that can destroy the organism. Once the body has identified a foreign organism and created antibodies for it, the immune system will retain a memory of the organism and destroy it whenever it enters the body again.

When confronted with bacterial infection, internists may recognize the organism that causes it from the patient’s symptoms, or they may have to take specimens from the site of inflammation and test them in order to identify the organism involved. Sometimes, the organism is identified by microscopic examination, often using a dye that stains certain bacteria. Sometimes, it is necessary to grow the organism in a culture medium in order to identify it. The organism may also be identified by its antigen or by the type of antibody that the immune system produces to fight it.

The signs of viral infection are often exactly the same as those of bacterial infection. The main difference is that the causative organism cannot be isolated and identified as easily. Unlike bacteria, viruses cannot be seen through a microscope or otherwise identified by many of the methods used for bacteria. They can be cultured, however, or antigens or antibodies may be detectable.

In addition to treating infectious diseases, internists are called on to treat dysfunction in all parts of the body. They treat many patients suffering from heart disease, the major killer of Americans. The heart is actually subject to a wide range of disorders, the most common and the most deadly of which is coronary artery disease. Internists have many means of diagnosing heart diseases and, often, predicting them. The patient’s presenting symptoms and an analysis of the patient’s lifestyle will often suggest the possibility of heart disease. Various in-office and laboratory procedures will inform the internist of the precise status of the patient’s heart function and help direct the course of therapy.

Cancer, the second most common cause of mortality in the United States, is often seen by internists. Lung cancer is the leading cause of cancer death, followed by cancer of the colon or rectum, breast, prostate gland, urinary tract, and uterus. The lymph system, blood, mouth, pancreas, skin, stomach, and ovary are also common sites. The term cancer describes a large number of disorders. What all cancers have in common is that the cells of an organ multiply uncontrollably. As the cancer cells proliferate, they crowd out other cells and interfere with organ function. Sometimes cancer cells from one organ spread to neighboring organs or are carried to other parts of the body. This process is called metastasis, and it can indicate that the cancer has spread or is spreading throughout the body. Internists may be responsible for treating cancer patients throughout the disease process or may refer them to oncologists, or cancer specialists.

Diseases of the respiratory system are major concerns of the internist. In addition to bacterial and viral infections, there are many acute and chronic respiratory conditions. One major example is asthma. Its cause is unknown, but it is believed to be at least partially attributable to allergy. When an asthma attack occurs, airways in the lungs swell and constrict. Mucus builds up and airflow is restricted, causing the patient to wheeze and gasp for air. Many internists have become skilled in helping asthmatic patients, alleviating symptoms, and preventing attacks.

All parts of the body harbor the potential for disease, infectious and otherwise. They are all, to some degree, the province of internists. The kidneys and the urinary system, the gastrointestinal system, the immune system, the endocrine glands, the brain and the nervous system, and the skeletal system are all within the internist’s broad purview. Often disorders in these various organs and systems can be treated fully by internists. When they believe that a patient needs a physician with greater knowledge in a particular area of medicine, however, internists will refer the patient to an appropriate specialist.

In addition to their diagnostic skills, internists must possess a wide knowledge of modern treatment modalities. Surgery is rarely among the procedures mastered by the internist, so surgical procedures are routinely referred to surgeons specializing in the particular techniques involved.

Primary among the internist’s tools for fighting infectious diseases are the antibiotics. These are the mainstays of therapy for infections caused by bacteria and other nonviral microorganisms. Since the first antibiotics were developed in the 1930s and 1940s, literally hundreds more have been developed. Scores of these are in use, and new agents are constantly being introduced.

It is vital for internists to keep abreast of new antibiotics because disease-causing organisms are often able to develop resistance against antibiotic agents that have been in use for a long time. For example, many strains of bacteria that were susceptible to penicillin have developed the ability to counteract its antibiotic effect. Other agents had to be found to destroy these resistant strains. This phenomenon occurs across virtually the entire range of the available antibiotics: prolonged use of a given agent often allows the target organism to develop resistance to it. Internists must also be skilled in the proper use of antibiotics. Knowing which agent or combination of agents to prescribe, in what amounts, and for how long are important considerations in developing the patient’s treatment plan. Antibiotics are not useful for treating viral infections, but there are a limited number of antiviral agents available for treating certain diseases.

Immunization against infectious diseases can be an important concern of the internist. The most extensive immunization programs in the United States are directed toward the vaccination of children and thus are generally carried out by pediatricians and family practitioners. Internists are often responsible, however, for the immunization of adult patients. Immunization against influenza is recommended for the elderly, particularly when a new strain of influenza virus arises. It is also recommended that elderly hospitalized patients be vaccinated against pneumococcal pneumonia. Internists are a primary avenue of immunization against hepatitis B, particularly among high-risk target populations, such as medical personnel, intravenous drug abusers, and adult male homosexuals. Internists are also involved in immunizing patients who require special vaccinations because of exposure to disease or for travel to foreign countries.

Patients who require long-term or lifelong therapy for noninfectious diseases include individuals with heart diseases, high blood pressure, diabetes, cancer, respiratory disorders, and a host of other conditions. The challenge to the internist is to develop a regimen that is both efficacious and safe. Drug therapy is prominent in the internist’s treatment armamentarium. In either short-term or long-term drug therapy, problems may arise. The patient may develop significant side effects or adverse reactions. The drug may lose its effectiveness after months or years of therapy. The condition may change and require dosage adjustments, additional medications, or a complete change of regimen.

Consistent monitoring of the patient’s condition is an important part of therapy. The internist wants to ensure that the prescribed regimen is working and that the therapy is comfortable for the patient. For example, the earliest agents for high blood pressure, or hypertension, often had such disagreeable side effects that patients would stop taking them. Hypertension has virtually no symptoms. After the patient started taking medication, however, he or she could experience loss of energy, listlessness, impotence, dream disturbances, and many other unwelcome effects. Similarly, diabetes patients who are dependent on regular insulin injections sometimes neglect their therapy. They may balk against sticking themselves with needles three or four times a day, and they may not monitor their blood sugar adequately. Preventing the devastating and potentially fatal consequences of diabetes depends on rigorous compliance with all aspects of the diabetes regimen, including diet, insulin, and monitoring.

Thus, patient compliance with therapy becomes one of the major tasks of the internist and virtually any other physician: If the patient does not cooperate with the regimen that the doctor prescribes, the therapy is not likely to be effective. For this reason, many internists now make patient counseling part of their practice. The modern internist recognizes that patients must understand their therapeutic goals, why they are being given certain medicines, and what these drugs can be expected to accomplish. Furthermore, many internists find that it is wise to alert their patients to possible adverse reactions, although they understand the necessity of not frightening the patient. Some internists find the time to discuss their therapeutic regimens thoroughly with their patients. Others use nursing staff or other health care workers to educate patients.

Treatment modalities change constantly, and internists are required to be aware of the latest advances in order to modify their therapy programs to take advantage of improvements in drugs or procedures. Not only are new drugs constantly being approved for use, but modern medical science is continually learning new facts about old diseases as well, and these new insights often radically alter the way a given disease is treated. A good example is a stomach ulcer. For years, it was thought that certain ulcers in the stomach were caused by erosion of the stomach wall by gastric juices. A group of investigators found, however, that a significant number of ulcer patients were also infected with the bacterium
Helicobacter pylori
. It has been suggested that infection may play a role in the development of these ulcers and that, therefore, therapy should be amended to include an antibacterial agent that is effective against H. pylori.

Furthermore, the internist’s patient load is changing. Most internal medicine practices are treating increasing numbers of elderly patients, who have special needs. Internists must be aware of the constant advances in geriatric medicine in order to modify therapy for older patients.

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