When you hear the word arthritis, you probably think about the major joints in the body where arthritis typically occurs: the hands, wrists, elbows, shoulders, knees, ankles and feet. Although rare, arthritis can strike visceral organs, such as the lungs, heart, sclera (outer covering) of eye, outside of the ears, heart, vocal cords, nervous system, abdominal walls and muscles. Other conditions may also cause arthritis to pop up in the most unlikely places.
Rheumatoid nodules
In particularly severe cases of arthritis, especially in people who tests positive for arthritis via a blood test, patients may develop rheumatoid nodules. They are the most common manifestations of arthritis outside of the joints. Nodules occur in 20 to 30 percent of patients with arthritis. They are small, firm lumps found under the skin. Nodules most often appear on the skin on the outer arms and elbows, or on pressure points on the feet and knees.
Psoriatic arthritis
Psoriatic arthritis is arthritis associated with psoriasis, which is also a chronic condition that causes itchy red patches on the skin. Although psoriatic arthritis usually affects the skin and nails, patients may also develop scaly skin on the scalp, bellybutton, between the buttocks, or on the heels and soles of the feet.
TMJ arthritis
The temporomandibular joint, or TMJ, is the joint that connect the lower jaw to the skull in front of each ear. It is a site for numerous disorders that affect speaking, facial expressions and biting, chewing and swallowing food. TMJ arthritis is common in people who have TMJ dysfunction. Patients with osteoarthritis may develop TMJ arthritis and it is sometimes a secondary condition of Rheumatoid Arthritis.
Reactive Arthritis
Like rheumatoid and osteoarthritis, reactive arthritis is also an inflammatory condition. It typically develops two to four weeks after a venereal or intestinal infection--although certain genes can increase the risk for this disease. Arthritis is the last symptom to appear following the infection. Reactive arthritis is usually temporary; however, about 20 percent of patients with reactive arthritis will go on to develop chronic arthritis.
Reactive arthritis may appear in parts of the urogenital system, such as the urethra, prostate, cervix, fallopian tubes, vulva and vagina. It occurs primarily in men under 40, and roughly 25 percent of men with reactive arthritis will develop shallow, painless lesions on their penis. Reactive arthritis symptoms may also appear on the lower back, buttocks, eye, soles of feet and the palms of the hands.
Sources
http://www.hopkins-arthritis.org/arthritis-info/rheumatoid-arthritis/rheum_clin_pres.html
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1479577/
http://www.arthritis.org/disease-center.php?disease_id=23&df=effects
http://www.nlm.nih.gov/medlineplus/ency/article/000440.htm
http://www.mayoclinic.org/tmj/rheumatoid.html
http://www.nidcr.nih.gov/OralHealth/Topics/TMJ/TMJDisorders.htm
