Immunologist vs. Rheumatologist: What's the Difference?

In the constellation of medical specialties, there can sometimes be overlap between the various doctors who treat certain conditions. For example, a cardiologist who's focused on keeping your heart healthy may call on a pulmonologist -- who specializes in taking care of the lungs -- for patients with congestive heart failure, pulmonary hypertension and other conditions that can involve both organ systems.

The same is true for the specialty fields of immunology and rheumatology. Though these two highly trained specialists often see different kinds of patients, sometimes they work together and must collaborate.

[Read: Have One Autoimmune Disease? You May Be at Risk for Another.]

What Is an Immunologist?

"Immunologists study the immune system," says Dr. Shirley W. Pang, a rheumatologist with St. Jude Medical Center in Fullerton, California. These individuals may go on to become scientists, conducting research into the immune system and how it works. But there are also "clinical immunologists, the MDs who treat patients with various conditions, such as asthma, allergies and disorders of the immune system," which are referred to as immunodeficiencies.

Also sometimes called allergists, immunologists, "diagnose, treat and manage various immunological conditions including allergies, asthma and immunodeficiency diseases, says Dr. Simranjit Singh, a rheumatologist at Mission Hospital in Orange County, California.

Common reasons to visit an immunologist include:

-- Asthma. Asthma causes the airways to narrow, swell and produce extra mucus. This can make breathing normally more difficult and trigger coughing, wheezing and shortness of breath. There's a strong connection between asthma and allergies, so an allergist or immunologist is often involved in the care of a patient with asthma, particularly if it's severe and a primary care doctor wants a specialist to intervene.

-- Food allergies. Eggs, peanuts, milk, shellfish and a variety of other food items can trigger potentially deadly allergic responses in certain individuals. If you have food allergies, you'll probably need to work with an allergist to determine which foods are in bounds and what's off limits.

-- Seasonal allergies. If you struggle with very severe seasonal allergies, you may need to visit with an allergist for relief. You may be able to get immunotherapy shots to help control your seasonal allergy symptoms.

-- Eczema and hives. Atopic dermatitis, or eczema, is an itchy rash that can be caused by exposure to an allergen. Urticaria's more common name is hives, and these itchy red welts can develop on the skin after exposure to an allergen.

-- Autoimmune diseases. In an autoimmune disease, the body's normally protective immune system goes haywire and begins attacking healthy cells. This can cause a range of diseases depending on where the inflammation is occurring, and an immunologist will often be involved in the diagnosis and treatment of these complex and often difficult-to-diagnose disorders.

[SEE: Lupus Diet and Nutrition.]

What Is a Rheumatologist?

On the other hand, a rheumatologist is usually the go-to specialist when you're dealing with a disease that affects a joint.

"Rheumatologists treat joint diseases similar to orthopedists, but do not perform surgeries," Singh explains. This aspect of the rheumatologist's work means they may treat people who have:

-- Osteoarthritis. The most common form of arthritis, this is a degenerative disorder that's related to age and wear-and-tear. Over time, the cushioning cartilage in joints wears away, and that leads to pain, stiffness and swelling.

-- Tendinitis. An inflammation of a tendon, tendinitis causes pain and swelling around a joint. It's often related to repetitive motion or trauma, such as may occur during sports activities.

-- Gout. This form of arthritis features sudden, severe attacks of pain, swelling, redness and tenderness in the joints, usually in the big toe.

You might also see a rheumatologist to treat certain autoimmune diseases, including:

-- Rheumatoid arthritis. This autoimmune condition causes pain, redness and swelling in one or more joints throughout the body. In addition, it can cause fever, fatigue and joint stiffness.

-- Lupus. Lupus, also called systemic lupus erythematosus, is an autoimmune disease in which the immune system mistakenly goes on attack against the body's own cells. Symptoms include severe fatigue, joint pain and swelling, blood clotting problems and headaches. A butterfly rash across the cheeks and nose is the hallmark symptom.

-- Vasculitis. This autoimmune disease causes inflammation of the blood vessels. It can lead to restricted blood flow that causes organ and tissue damage. Pain, fatigue and fever are common symptoms.

-- Scleroderma. This group of rare autoimmune diseases causes the skin to harden and tighten. It can also cause damage to the lungs and kidneys.

-- Psoriatic arthritis. This inflammatory type of arthritis is related to the common skin disorder psoriasis, which is an autoimmune disease that affects the skin. Psoriatic arthritis causes joint and foot pain, swelling in the fingers and lower back pain.

-- Ankylosing spondylitis. This inflammatory disease causes small bones in the spine to fuse. It leads to a hunched-over posture.

[Read: How to Deal With Arthritis Pain in the Hands.]

The Two Specialties Sometimes Overlap

In some cases, rheumatologists and immunologists work closely together to help a patient with specific issues, particularly "for more complicated cases" that are resistant to treatments or are more severe, Pang says. "Also, our autoimmune patients tend to be predisposed to allergies, asthma and eczema, so oftentimes are referred to allergists and immunologists for a work up for this, as well as treatment," she adds.

If the two specialties were placed in a Venn diagram, Dr. Bharat Kumar, an immunologist and rheumatologist who serves as associate rheumatology fellowship program director in the division of immunology at the University of Iowa Hospitals and Clinics in Iowa City, Iowa, would be right in the middle of the overlapping area.

Kumar says that because he's dual-certified in rheumatology and immunology, he sees both rheumatology patients and immunology patients. He's also one of about 70 specialists across the U.S. who are dual-certified in these two specialty areas, and as such, can provide useful assistance in cases where a patient needs the care of both types of physicians.

"Originally rheumatologists were focused on musculoskeletal conditions," such as osteoarthritis. "But the more we learn about the causes of these diseases, the more we've learned that's an immune angle. So, rheumatologists became a lot more like immunologists in that case." And as science learns more about the causes of some of these diseases, "the overlap between the two specialties is growing more and more," Kumar says.

"We're learning that a lot of the disorders that we've classically called autoimmune disorders because the immune system is overactive are associated with very subtle other immune derangements that allergists and immunologists have been seeing. So now there's a lot more cooperation between the two specialists to identify and manage these people," who may be experiencing a wide range of symptoms related to both rheumatological and immune disorders.

"We are realizing, for example, that there is a very close connection between asthma and rheumatoid arthritis, something that previously was not fully appreciated. So, these kinds of unexpected links are bringing allergists and rheumatologists together in ways we didn't anticipate even five to 10 years ago," Kumar says.

In particular, the overlap between the immunologists and rheumatologists can be helpful "when it comes to finding a balance in the immune system," Singh says. "Oftentimes, patients can have multiple conditions going on, and different medications used by the two specialties are sometimes needed to find a balance."

Many medications used to treat rheumatological conditions "are immunologically active," Kumar says. "So, it might be a good idea to incorporate an immunologist into care for people who are taking these immune-active medications."

"In addition, monitoring treatments for different signs and symptoms may require a rheumatologist as well," Kumar.

This dual-specialty care approach may be particularly important for people with certain kinds of autoimmune diseases that can cause problems in the joints and musculoskeletal system, such as:

-- Systemic lupus erythematosus. Also called SLE or just lupus, systemic lupus erythematosus may require the assistance of both a rheumatologist and an immunologist.

-- Common variable immune deficiency. Also called CVID, this disorder is an antibody deficiency that means the immune system can't fully protect the body from pathogens, such as bacteria or viruses. It's also sometimes referred to as acquired hypogammaglobulinemia, common variable hypogammaglobulinemia, common variable immunodeficiency, CVI or late-onset immunoglobulin deficiency. The body doesn't make enough of immunoglobulins, a type of protein that fight off infections.

-- Fibromyalgia. Fibromyalgia is a widespread musculoskeletal pain disorder. It causes fatigue, widespread pain and cognitive difficulties. No one is certain what causes it. It's not classified as an autoimmune disorder, but it bears some similarities to such diseases.

-- Mast cell activation syndrome. In this syndrome, the mast cells -- also called allergy cells that are part of the immune system -- release too many chemical mediators. It can lead to anaphylaxis, and other severe allergic symptoms.

If you have any of these conditions, Kumar recommends that you "talk to your rheumatologist or immunologist about evaluation and referral," if that's warranted.