Rheumatoid arthritis and osteoarthritis: Pathology review

Jody is a 55 year old woman who presents with a 6 month history of bilateral hand and wrist stiffness.

She mentions that the stiffness lasts for more than an hour a day but tends to improve as she uses the affected joints.

Examination shows swelling, limited range of movement, and subcutaneous nodules over the proximal interphalangeal joints, but no redness.

Then you see Kerry, a 60 year old woman who comes in with a 1 year history of pain in the right knee that has gotten progressively worse.

The pain is worse in the evening or with use of the affected limb and is associated with stiffness, which typically occurs at rest and lasts around 10 to 15 minutes.

Examination reveals Kerry is obese, has bowing of the right knee, and that the affected joint has a limited range of motion.

Blood tests are ordered in both cases, showing in Jody's case high levels of rheumatoid factor (RF) and anti-citrullinated peptide antibody (ACPA), whereas in Kerry's case both antibodies were absent.

Both people have arthritis.

Now, a healthy joint usually consists of two bones, each with its own layer of articular cartilage.

Articular cartilage is a type of connective tissue with a lubricated surface that acts like a protective cushion for bones to smoothly glide against.

Now, there are many types of joints, including fibrous, cartilaginous, and synovial joints, which have additional components depending on their function.

For example, synovial joints, like those of the wrist, elbow, knees, shoulders, and hips, are mobile joints that connect two bones via a fibrous capsule that is continuous with the periosteum, which is the outer layer of bones.

The fibrous capsule is lined with a synovial membrane that has cells that remove debris and produce synovial fluid, which is a viscous fluid found inside the joint capsule to lubricate the joint.

Together, the synovial membrane and articular cartilage form the inner lining of the joint space.

Now, arthritis refers to a group of diseases that cause destruction of one or more joints, and it can be classified as inflammatory or non-inflammatory.

Inflammatory arthritis is caused by an )immune response attacking the joints.

It includes conditions with unknown cause, like rheumatoid arthritis and juvenile idiopathic arthritis, or it can be secondary to diseases like systemic lupus erythematosus and Sjogren syndrome.