Mixed Connective Tissue Disease (MCTD)

This is the first in a series of posts about diseases that are either very similar to, or often associated with, lupus. I plan to cover both Raynaud’s and Sjögren's syndromes in subsequent posts. 

Diagnosing Difficult Cases

While it would be nice to say that each autoimmune disease has separate and distinct symptoms, the fact is that there is a great deal of overlap between them. This makes diagnosing diseases quite difficult. If I have enough symptoms to be diagnosed with lupus but I also have symptoms more commonly seen in rheumatoid arthritis (RA) should I also be diagnosed with RA? Would it be better for my doctor to say instead that  I just have unusual lupus symptoms? And if RA and lupus are treated the same way, does it even matter?

The fact is that biology doesn’t conform well to hard and fast rules. The immune system is particularly difficult this way; I used to tell my undergraduate immunology students that every rule they learned in class would have an exception somewhere. Since the immune system itself doesn’t follow strict rules, it should come as no great surprise that autoimmune diseases don’t either. I regard autoimmune diseases as being points on a continuum, rather than existing as discrete entities. These diseases all share in common the fact that the immune system has lost the ability to tell whether various tissues in the body are part of the body or whether they are invading germs. Specific autoimmune diseases are diagnosed depending on which parts of the body are being attacked, and by which parts of the immune system are doing the attacking.

Most people with autoimmune diseases have enough symptoms specific to a specific disease to receive a specific diagnosis. But for some, their symptoms really don’t fit neatly into a disease category. These people are often diagnosed with Mixed Connective Tissue Disorder, or MCTD. It is not uncommon for people with MCTD to initially be diagnosed with, for example, lupus. Often it takes time for distinctly non-lupus like symptoms to appear. Only after it is clear that the symptoms do not all fit into one disease that a doctor will give the MCTD diagnosis.

What is connective tissue, anyway?

Connective tissues are the tissues and structures in the body that serve to, you guessed it, connect different parts of the body. Tendons and ligaments are perhaps the most commonly known forms of connective tissue, but there are others. Even blood can be considered connective tissue, since it does connect and support various different organs.

Because there are so many different kinds of connective tissue, connective tissue diseases can manifest themselves in all sorts of different ways. Some people experience joint pain as the tendons keeping the joints together get attacked by the immune system. Others may have muscle problems as various muscles in the body are damaged by the immune system.

            Connective tissue literally holds the body together. This is why connective tissue diseases are so serious, and why they are treated with powerful immunosuppressants or corticosteroids.

UCTD vs MCTD?

There is some debate as to whether MCTD is the same thing as Undifferentiated Connective Tissue Disorder (UCTD). I’m going to use the Mayo Clinic’s classification, which says that the two are different.

UCTD:

The American College of Rheumatology has (somewhat arbitrarily, in my personal opinion), come up with a list of eleven symptoms that are used to diagnose lupus. Generally, a patient needs to experience at least four of the eleven symptoms to receive a formal diagnosis of systemic lupus. This can lead to a diagnostic dilemma: How should a physician diagnose somebody who has at least one, but fewer than four, symptoms?

The answer, for many physicians, is to give a diagnosis of UTCD. It is often followed by a more specific diagnosis, once more symptoms have appeared. The UCTD diagnosis is generally the physician’s way of saying, “This patient has symptoms of an autoimmune disorder, but I can’t quite classify it as a specific disease yet.” UCTD patients are often, although not always, diagnosed with lupus later on.

MCTD:

MCTD is a smorgasbord (or “overlap” if you want to be more technical) disease. It manifests in a variety of ways common to lupus, rheumatoid arthritis, polymyositis and scleroderma. Like lupus, it can lead to serious problems. For example, inflammation from both diseases may lead to heart disease and/or other cardiac complications. Lupus and MCTD can also both lead to Raynaud’s disease, a condition in which blood vessels prevent blood flow to the hands and feet.

The difference between the lupus and MCTD is hazy at best. Symptoms of lupus can be present in MCTD as well. However, not all MCTD symptoms fit into the lupus definition. If someone who was diagnosed as having lupus starts showing signs of, for example, unusual connective tissue growth (which is more common to scleroderma), (s)he may be rediagnosed as having MCTD. The new diagnosis is broader, and allows for symptoms from several related diseases.

So which is more serious, lupus or MTCD?

            It’s impossible to say. Both diseases describe such a wide variety of symptoms and a huge amount of variation between patients that ranking one over the other is impossible. My personal belief is that it’s a tie. Both cause inflammation, both are treated with similar drugs, and both can cause everything from a minor to fatal illnesses. 

The take home message? Autoimmune diseases suck, but at least they suck in a variety of strange and unusual ways.

Additional legal notes:
1) Much of the information presented here is from the mayo clinic and the ACR. Links are provided in the text.
2) My usual disclaimer applies. I am not a physician, nor can I promise that my brain fog will allow me to write without making mistakes. Please do not ever use my explanations as a substitute for talking to your doctor!