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Subspecialists in internal medicine have chosen to receive additional, more in-depth training and board certification in the diagnosis and management of diseases of a specific type (e.g., infectious diseases) or diseases affecting a single organ system (e.g., the heart). Although subspecialists often see patients for a limited basis in consultation from a general internist or another medical specialist, they too may develop long and rewarding relationships with patients who have ongoing or chronic illnesses that demand continued care.

Once general internal medicine residency training is complete, a physician may begin to practice internal medicine. Alternatively, many physicians wish to obtain further subspecialty training in a more limited area with a plan to focus their future activities on diseases of one type or organ system. Subspecialty training, called fellowship, usually adds two to three years after medical residency. Applications for fellowship are generally submitted during the second year of the internal medicine residency.

Although the complex structure of internal medicine may seem confusing, in many ways it reflects the breadth and richness of internal medicine as a discipline and the subspecialty areas of internal medicine are worth exploring as you begin to think about your career choice.

Remember that the basic training in internal medicine is 3 years after medical school (see How Internal Medicine is Structured). Completion of this training enables you to be board-certified in internal medicine and practice general internal medicine. General internists may practice primary care, serve as hospitalists, or provide both types of care in a variety of practice models.

However, at least half of internists completing their basic residency training will continue with further training to focus their expertise in a specific area of internal medicine. Here are some important things to know about subspecialty training in internal medicine:

    • There are about 10 different internal medicine subspecialties, although this number varies since sometimes training in specific areas may be combined with each other into a single training program. For example, individual training programs are available for both hematology and oncology, but these programs are frequently combined into a single training program (hematology and oncology) that prepares trainees for board certification in both areas.

    • Subspecialty trainees are typically referred to as “fellows” (as opposed to “residents,” who are trainees in their basic field of study [such as internal medicine], and “interns,” who are residents in their first year of training after medical school). These fellows also differ from being a Fellow in the American College of Physicians (FACP), which is a designation reserved for internists who have documented advanced achievement in their clinical or academic careers in internal medicine—you may see this designation in some of your attendings’ academic titles, with the letters "FACP" following the "MD."

    • The time that it takes to complete a fellowship in an internal medicine subspecialty varies greatly among different areas of training (see the Internal Medicine Training Flowchart). Some programs may be completed in a time period as short as 1 year, while others may be up to 3 years. Additionally, some individuals choose to continue with additional training beyond the basic subspecialty program. For example, basic cardiology fellowship training is 3 years; however, if you are interested in developing additional expertise in specific areas of cardiology, such as performing specific procedures or cardiac electrophysiology, an additional year of training is available.

    • Although the way training is structured makes it seem as though becoming a subspecialist can be an incredibly long process, remember that all subspecialty trainees are already internists and are full-fledged physicians when they start fellowship training. Therefore, subspecialty training represents an advanced form of practice, with trainees fully able to practice and essentially already working in their area of interest. Because of this, most fellows find their fellowship training to be an intensive but extremely rewarding time in their careers.

    • Once a trainee has completed subspecialty training, they are often referred to by the name of the discipline in which they have gained additional expertise. For example, someone who has finished a pulmonary and critical care fellowship may be called a “pulmonologist” or “intensivist” (if they work in a critical care unit). However, every subspecialist is an internist, since they have completed basic training in internal medicine.

    • The different subspecialties of internal medicine are extremely different and varied. Reflecting the breadth of internal medicine as a clinical discipline, the internal medicine subspecialties each have a unique skill set and clinical outlook focusing on the types of patients who they treat. For example, some subspecialties (such as endocrinology, infectious disease, and rheumatology) deal with disorders that affect many systems in potentially subtle ways and require the ability to diagnose and manage these types of diseases. Other subspecialties are more focused on specific organ systems (such as cardiology and gastroenterology) and may have individuals practicing in those areas who are very procedurally oriented (such as interventional cardiologists and therapeutic endoscopists). Each subspecialty within internal medicine is very unique, and it is worth exploring what exactly they do.

    • Pursuing a subspecialty doesn’t mean that you can only practice within that area. Although many subspecialists do choose to see only patients with specific problems within their area, many subspecialists continue to use their general internal medicine skills in their subspecialty practice. This is why internal medicine is structured as it is—specific diseases always occur in the context of an overall patient, and it is necessary to understand the relationship of those disorders to the rest of the system, which is what is learned in basic internal medicine training. Completing subspecialty training does not preclude you from practicing general internal medicine, as you have already completed that training. Because of this, some subspecialists work as hospitalists or maintain “split” practices, seeing both general medical patients and those with problems in their area of subspecialty expertise.

It is necessary to understand the subspecialties fully understand the breadth and depth of internal medicine. If you think that you might have an interest in what internal medicine subspecialists do, feel free to talk to them about what they do and what their career and lifestyle is like. More information about the internal medicine subspecialties is available below, and each of the subspecialties has its own practice society where you can learn more.

Core Subspecialities
  • Cardiovascular Disease/Cardiology
    Cardiology is the prevention, diagnosis, and management of disorders of the cardiovascular system, including ischemic heart disease, cardiac dysrhythmias, cardiomyopathies, valvular heart disease, pericarditis and myocarditis, endocarditis, congenital heart disease in adults, hypertension, and disorders of the veins, arteries, and pulmonary circulation.

  • Clinical Cardiac Electrophysiology
    Clinical Cardiac Electrophysiology is a branch of Cardiology that manages complex cardiac arrhythmias with the use of implantable pacemakers and cardioverter-defibrillators, and also applies other interventional techniques and treatments.

  • Critical Care Medicine
    Critical care medicine encompasses the diagnosis and treatment of a wide variety of clinical problems representing the extreme of human disease. Critically ill patients require intensive care by a coordinated team. The critical care specialist (intensivist) may be the primary provider of care or a consultant. The intensivist needs to be competent not only in a broad range of conditions common among critically ill patients but also with the technological procedures and devices used in the intensive care setting.

  • Endocrinology, Diabetes and Metabolism
    Endocrinology is the diagnosis and care of disorders of the endocrine system. The principle endocrine problems include goiter, thyroid nodules, thyroid dysfunction, diabetes mellitus, hyper- and hypocalcemia, adrenal cortex dysfunction, endocrine hypertension, gonadal disorders, disorders of sodium and water balance, manifestations of pituitary disorders, disorders of bone metabolism, and hyperlipidemia.

  • Gastroenterology
    Gastroenterology encompasses the evaluation and treatment of patients with disorders of the gastrointestinal tract, pancreas, biliary tract, and liver. It includes disorders of organs within the abdominal cavity and requires knowledge of the manifestations of gastrointestinal disorders in other organ systems, including the skin. Additional content areas include nutrition and nutritional deficiencies, and screening and prevention, particularly for colorectal cancer.

  • General Internal Medicine
    Internal medicine is a specialty that relies on the basic sciences and a diverse breadth of knowledge to form the foundation for a successful career in a variety of fields, including general internal medicine, hospital medicine, or any of the internal medicine subspecialties. Specialists in general internal medicine (“general internists”) are crucial in filling a vital need in our health care system, serving as the primary or principal providers of care in outpatient (ambulatory) and /or inpatient (hospital) settings.

  • Geriatric Medicine
    Geriatric medicine involves the recognition of differences in presentation of disease and the importance of maintaining functional independence in elderly patients. Geriatrics is a primary care discipline oriented toward preventive, routine, acute, and chronic medical care of elderly patients.

  • Hematology
    The discipline of hematology relates to the care of patients with disorders of the blood, bone marrow, and lymphatic systems, including the anemias, hematological malignancies and other clonal processes, and congenital and acquired disorders of hemostasis, coagulation, and thrombosis.

  • Infectious Disease
    Infectious disease medicine requires an understanding of the microbiology, prevention, and management of disorders caused by viral, bacterial, fungal, and parasitic infections. This understanding includes the appropriate use of antimicrobial agents, vaccines, and other immunobiological agents. Important content includes the environmental, occupational, and host factors that predispose to infection, as well as the basic principles of epidemiology and transmission of infection.

  • Interventional Cardiology
    Interventional Cardiology is the branch of Cardiology responsible for catheter-based interventions in the management of ischemic heart disease, congenital heart disease, and acquired valvular disease.

  • Medical Oncology
    Medical oncology is the subspecialty which involves the diagnosis and management of benign and malignant neoplasms. Oncologists typically identify individuals at risk for malignancy and counsel them regarding risk reduction and screening, investigate clinical symptoms and syndromes suggestive of underlying malignancy, identify and treat neoplasms with a potential for cure, and undertake the care of patients with solid and hematologic tumors to prolong life and/or palliate symptoms.

  • Nephrology
    Nephrology involves the diagnosis and management of diseases of the kidneys, the contiguous collecting system, and the associated vasculature.

  • Pulmonary Disease
    Pulmonary medicine is the diagnosis and management of disorders of the lungs, upper airways, thoracic cavity, and chest wall. The pulmonary specialist has expertise in neoplastic, inflammatory, and infectious disorders of the lung parenchyma, pleura and airways; pulmonary vascular disease and its effect on the cardiovascular system; and detection and prevention of occupational and environmental causes of lung disease. Other specialized areas include respiratory failure and sleep-disordered breathing.

  • Rheumatology
    Rheumatology deals with the prevention, diagnosis, and management of crystalline diseases, systemic rheumatic diseases, spondyloarthropathies, vasculitis, inflammatory muscle disease, osteoporosis, osteoarthritis, recreational sports injury, soft-tissue diseases and trauma. The goal of the rheumatologist is the early diagnosis and treatment of these conditions to prevent disability and death.

  • Sleep Medicine
    Physicians who specialize in Sleep Medicine are trained to detect, treat, and prevent sleep disorders, such as obstructive sleep apnea, snoring, insomnia, sleep walking, and jet lag.

  • Transplant Hepatology
    Transplant Hepatology training involves one year of additional clinical training after completion of both residency in internal medicine and fellowship training in gastroenterology. Candidates must also complete the following procedural requirements: performance of at least 30 percutaneous liver biopsies, including allograft biopsies; interpretation of 200 native and allograft liver biopsies; and knowledge of indications, contraindications, and complications of allograft biopsies.

Affiliated Subspecialties
  • Adolescent Medicine
    Adolescent medicine focuses on the physical, psychological, social, and sexual development of adolescents and young adults. Multidisciplinary and comprehensive in approach, this specialty encompasses the full spectrum of acute, chronic, and preventive health care.

  • Allergy and Immunology
    Allergy and immunology involves the management of disorders related to hypersensitivity or altered reactivity caused by the release of immunologic mediators or by activation of inflammatory mechanisms.

  • Hospice and Palliative Medicine
    Palliative medicine aims to relieve symptoms and pain a patient suffers due to a serious illness. Goals of palliative care include reducing suffering, improving the quality of life for a patient, and supporting the patient and family throughout the treatment process.

    Hospice care is provided for patients facing a terminal diagnosis who no longer wish to undergo curative treatment. Goals of hospice care include relieving symptoms and supporting patients in the end-of-life stages.

  • Sports Medicine
    The discipline of sports medicine primarily concerns itself with the emergency assessment and care of acutely injured athletes, diagnosis, treatment and management of common sports injuries and illnesses, management of medical problems of the athlete, rehabilitation of ill and injured athletes, and exercise as treatment.

Combined Programs
  • Combined Internal Medicine and Pediatrics
    Combined Internal Medicine and Pediatrics (Med-Peds) is the dual training in and dual practice of Internal Medicine and Pediatrics. Physicians practicing Med-Peds see both adults and children in a wide variety of practice settings and practice styles. Practice settings range from outpatient primary care to inpatient hospitalist practice, and practice styles range from urgent acute illness care to the longitudinal chronic illness care of patients with congenital heart disease.

IM Essentials

IM Essentials brings the self-assessment questions currently in MKSAP for Students and the textbook content of Internal Medicine Essentials for Clerkship Students together into a single, updated and integrated suite of educational materials with a variety of new enhancements. Learn more.

Benefits of ACP Membership for Students: ACP's free Medical Student Membership includes benefits designed especially to meet students' needs.

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Search ACP's Internal Medicine Residency Database for information on all internal medicine residency programs in the U.S. and Canada. (ACP Members only)

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