Arthritis mutilans, or pencil-in-cup deformity, is a rare form of psoriatic arthritis. It typically affects your fingers and toes, deforming and curling them. Read on to learn more about this condition including its causes, symptoms, diagnosis, and treatment.
What Is Arthritis Mutilans?
Also known as the pencil-in-cup deformity, arthritis mutilans is the most severe form of psoriatic arthritis. Arthritis mutilans occurs in 5 percent of people with psoriatic arthritis and affects your fingers and toes.
If you have this condition, your fingers and toes will become shorter due to bone degeneration. You may also develop ankylosis, which means your bones will fuse together.
As a form of psoriatic arthritis, arthritis mutilans happens when your immune system starts to attack healthy tissue and cells. This results in joint inflammation and the overproduction of skin cells.
It’s uncertain why your immune system would suddenly attack healthy cells and tissue, but a mixture of genetic and environmental factors is likely to play a role. Many people with psoriatic arthritis have family members who have the condition, and research has indicated that people with the HLA-B27 or DQB1*02 genes are more likely to develop this condition.
If you have these genes, the following may trigger the development of arthritis mutilans:
- Something in the environment
- Physical trauma
You may also develop psoriatic arthritis if you have psoriasis — a skin condition that gives you patches of red skin with white scales.
You may have arthritis mutilans if you experience the following symptoms:
- Severe joint pain and swelling in your hands and feet
- Bones in your hands and feet fuse and disappear
- Skin lesions, which usually appear before arthritis develops
- Nail changes, such as thickening and lifting from the nail bed (subungual hyperkeratosis) and discoloration (oil drop sign)
- Over time, you may get “opera glass hand,” which means your fingers can be pulled in and out like opera glasses due to unstable joints and bones
Arthritis mutilans usually appears in people aged 40 to 50 years old, but may also occur in other age groups, such as children and older adults.
If you’re experiencing these symptoms, contact your doctor immediately to get a proper diagnosis, since this condition can permanently deform your hands and feet if not treated in time.
Doctors currently use the Classification Criteria for Psoriatic Arthritis (CASPAR) to diagnose psoriatic arthritis. Even though psoriatic arthritis is a distinct condition, it’s underdiagnosed due to its wide range of symptoms. It’s estimated that more than half of people with the condition are undiagnosed.
Based on data drawn from 30 rheumatology clinics in 13 different countries, CASPAR is meant to be a guide for doctors to spot psoriatic arthritis before it progresses too far.
To be diagnosed with arthritis mutilans, you must have inflammatory arthritis in your:
- The connective tissue between your bone and ligaments or tendons (enthesis)
A rheumatologist or dermatologist will determine whether you have arthritis mutilans by asking you the following questions. You will be diagnosed with the condition if you have three or more points from the categories below:
- Evidence that you currently have psoriasis (2 points)
- Evidence that you have a history of psoriasis or a family history of psoriasis (1 point)
- Nail conditions typical of psoriasis, such as thickening of the skin under your nails (hyperkeratosis) or detached nails (onycholysis) (1 point)
- Negative test result for rheumatoid factor using any method other than latex (1 point)
- Current swelling of an entire toe or finger (dactylitis) or a history of dactylitis (1 point)
- X-ray evidence showing new bone growth near a joint (1 point)
You have moderate or severe arthritis mutilans if you have:
- At least three painful and swollen joints for more than six months
- Psoriatic skin lesions
- A history of psoriasis
The goal of treating arthritis mutilans is to:
- Alleviate pain
- Preserve joint structure
- Prevent bone deterioration
- Improve your ability to move your hands and feet
People with arthritis mutilans will also be given psychological counseling and physiotherapy.
Non-steroidal anti-inflammatory drugs. Doctors will typically prescribe non-steroidal anti-inflammatory drugs (NSAIDs) to treat milder forms of arthritis mutilans.
Disease-modifying antirheumatic drugs. These drugs, known as DMARDs, include methotrexate, cyclosporine, leflunomide, and others.
A weekly dose of methotrexate is usually effective in treating your pencil-in-cup deformity, but treatment depends on the severity of your condition and your medical history. However, methotrexate may cause liver damage if used with NSAIDs.
Cyclosporine is another common drug used to treat arthritis mutilans. It’s more effective when used with adalimumab, an anti-tumor necrosis factor agent.
Anti-tumor necrosis factor agents. This form of treatment is for people with moderate to severe arthritis mutilans who have an intolerance to NSAIDs or DMARDs for more than three months.
Surgery. This is the least common form of treatment for arthritis mutilans. One study found that only 7 percent of people with psoriatic arthritis needed surgery.