While rheumatoid arthritis (RA) is the most common form of inflammatory arthritis, the diagnosis is not always easy to make. The reason is that there are more than 100 different kinds of arthritis. Most of them involve inflammation. When a patient goes to a rheumatologist to get a diagnosis, there is a process of elimination in order to arrive at the proper diagnosis. This process of elimination is called “differential diagnosis.”
Differential diagnosis can be a difficult undertaking because so many forms of arthritis, particularly inflammatory forms of arthritis look alike. Generally it is helpful to divide the differential diagnosis of rheumatoid arthritis into two groups. The first group are the non-infectious diseases to consider and the second group are the infection-related conditions.
In part 1 of this article, I discussed the non-infectious causes of arthritis that need to be considered when assessing a patient with possible rheumatoid arthritis. In this article I will discuss those types of arthritis that are directly or indirectly due to infections.
Many infections can present with arthritis due to either direct inoculation of a joint (either from the outside or from a bloodstream infection) or due to autoimmune reactions. In many instances, infections lead to acute single joint arthritis; however, in some cases, chronic single or multiple joint arthritis can be present.
Missed infections can lead to significant complications; therefore, it is important to have a high index of suspicion for infection in any patient presenting with acute or chronic arthritis.
Here are some examples:
Gonococcal arthritis is an infection due to the organism that causes gonorrhea (N. gonorrhea). It usually affects a single joint (in 90% to 95% of cases). Symptoms include:
o Joint pain that migrates (jumps around) for 1 to 4 days;
o Pain in the hands/wrists due to inflammation of tendons;
o Sometimes a single joint can be inflamed;
o Skin rash;
o Burning on urination;
o Lower abdominal pain.
The diagnosis of gonorrhea is made by taking the history and by culture or DNA polymerase chain reaction (PCR) analysis of areas of possible infection, including the throat, genitals, and anus. Since the organism that causes gonorrhea is difficult to grow, it can often be missed on culture. Gonococcal arthritis can usually be distinguished from rheumatoid arthritis (RA) by clinical presentation, blood tests, and cultures.
Lyme disease is a bacterial infection due to the spirochete Borrelia burgdorferi. It presents with a skin rash, swollen joints and flu-like symptoms, caused by the bite of an infected tick. Symptoms may include:
o A skin rash, often resembling a bulls-eye; the rash may be more widespread, though;
o Muscle pain;
o Stiff neck;
o Numbness and tingling
o Bell’s palsy
o Swelling of knees and other large joints.
The diagnosis of Lyme disease is typically made by blood tests. Standardization of Lyme tests has improved greatly in the last few years. If chronic single joint arthritis develops, joint fluid analysis or joint tissue biopsy may be necessary for diagnosis. Lyme arthritis can usually be distinguished from RA by clinical presentation and blood testing.
Acute rheumatic fever (ARF) is an inflammatory disease that may develop after an infection with Streptococcus, the bacteria that causes strep throat and scarlet fever. The disease can affect the heart, joints, skin, and brain. Symptoms include:
o Arthritis (mainly affecting the knees, elbows, ankles, and wrists);
o Skin rash and skin nodules;
o A peculiar movement disorder, called Sydenham’s chorea;
o Epistaxis (nosebleeds);
o Heart problems;
o Abdominal pain;
ARF is diagnosed by history, physical exam, and blood testing for antibodies against streptococcus. ARF and RA can have similar clinical features including arthritis and nodules. But, ARF can usually be distinguished from RA. For instance, rash and migratory arthritis (arthritis that moves from joint to joint) are unusual in RA. Blood tests are also useful for making the distinction.
Bacterial endocarditis (BE) happesn when bacteria from the skin, mouth or intestines enter the bloodstream and infect the heart valves and heart lining. Symptoms include fever, chills, and other flu-like symptoms as well as unexplained weight loss and weakness. Diagnosis is made by blood cultures and ultrasound imaging of heart valves. Rheumatoid factor can be elevated in endocarditis, so it is not useful for distinguishing BE from RA.
Arthritis may be a symptom of many viral illnesses. The duration is usually short. Clinical features in adults include:
Joint symptoms occur in up to 60%. Joint pains are more common than true joint inflammation. The joint pains usually don’t last long. They are symmetric, and affect small joints of the hands, wrists, knees, and ankle joints. Morning stiffness and swelling can be present. A rash may be present
The most common cause of viral arthritis is probably Parvovirus B19.
Diagnosis of viral arthritis is usually made by blood testing.
RF testing is not helpful in distinguishing between hepatitis C infection and RA because RF levels can be elevated in patients with hepatitis C. However, in these situations, testing for anti-cyclic citrullinated peptide (anti-CCP) can be useful since these antibodies are not significantly elevated in hepatitis C infections.