Pencil-in-cup deformity is a rare bone disorder primarily associated with a severe form of psoriatic arthritis (PsA) called arthritis mutilans. It can also occur with rheumatoid arthritis (RA) and scleroderma. “Pencil-in-cup” describes what the affected bone looks like in an X-ray:

  • The end of the bone has eroded into a sharpened pencil shape.
  • This “pencil” has worn away the surface of an adjoining bone into a cup shape.

Pencil-in-cup deformity is rare. Arthritis mutilans affects only about 5 percent of people with PsA and 4.4 percent of people with rheumatoid arthritis. We’ll mainly look at pencil-in-cup deformity with PsA.

If your X-rays or scans show any signs of pencil-in-cup degeneration, it’s important to begin treatment as soon as possible to slow or stop further degeneration. Without treatment, joint destruction can proceed rapidly.

The first joints to be affected are often the second and third finger joints (distal interphalangeal joints). The condition can also affect your toe joints.

Although pencil-in-cup deformity is most commonly seen in PsA, other forms of arthritis that affect the bones of your spine and limbs (spondyloarthropathies) can also cause this disorder of the fingers and toes. As well, it occurs rarely in:

Arthritis mutilans and its characteristic pencil-in-cup deformity are the most severe form of untreated PsA.

The causes of PsA aren’t fully understood. It’s considered to be a complex interaction of genetics, immune system dysfunction, and environmental factors. About 30 percent of people with psoriasis develop PsA.

Having a family history of psoriasis increases your risk of getting psoriasis and PsA. But there are distinct genetic differences between psoriasis and PsA. You’re three to five times more likely to inherit PsA than you are to inherit psoriasis.

Genetic research has found that people with PsA who have two specific genes (HLA-B27 or DQB1*02) have an increased risk of developing arthritis mutilans.

Environmental factors thought to contribute to PsA include:

  • stress
  • infections (such as HIV or streptococcal infections)
  • trauma to joints (especially with children)
Share on Pinterest
‘Pencil-in-cup deformity is a rare bone disorder. An X-ray of this deformity shows the affected bone with the end of the bone eroded into a sharpened pencil shape. This “pencil” has worn away the surface of an adjoining bone into a cup shape. ‘

People who have pencil-in-cup deformity stemming from PsA may experience the symptoms of this form of arthritis. The symptoms of PsA are varied and can resemble those of other diseases:

  • swollen fingers or toes (dactylitis); studies found dactylitis present in 32 to 48 percent of people with PsA
  • joint stiffness, inflammation, and pain, usually in four or fewer joints and asymmetric (not the same joint on both sides of your body)
  • nail changes, including pitting and separation of nails from the nail bed
  • inflammatory neck pain
  • inflammatory arthritis of the spine and large joints (spondylitis)
  • inflammation of one or both sacroiliac joints (sacroiliitis); one study found that 78 percent of people with PsA had sacroiliitis
  • inflammation of the entheses, the places where tendons or ligaments enter your bones (enthesitis)
  • inflammation of the middle layer of the eye, causing redness and blurred vision (uveitis)

If you have pencil-in-cup deformity, you may also have these symptoms:

  • increased mobility of the tissue overlying the joint
  • severe bone destruction (osteolysis)
  • “opera glass” or “telescopic” fingers, in which the bone tissue collapses, leaving only skin

PsA often goes undiagnosed, because of its varied symptoms and a lack of agreement on criteria. To help standardize diagnosis, an international group of rheumatologists developed criteria for PsA known as CASPAR, classification criteria for psoriatic arthritis.

One of the difficulties is that arthritis occurs before skin psoriasis symptoms in 6 to 18 percent of people with PsA. So skin symptoms may not provide a clue. In addition, symptoms of psoriasis and PsA aren’t constant — they can flare and subside.

Your doctor will take a medical history, including your family’s medical history. They’ll ask you about your symptoms:

  • How severe are they?
  • How long have you had them?
  • Do they come and go?

They will also conduct a thorough physical examination.

To confirm a diagnosis of arthritis mutilans and pencil-in-cup deformity, your doctor will use more than one kind of imaging test, including:

  • X-ray
  • sonograph
  • MRI scan

Your doctor will look for severity of bone destruction. Sonography and MRI imaging can provide a finer picture of what’s going on. Sonography, for example, might detect inflammation that as yet has no symptoms. MRI can give a more detailed picture of small changes in your bone structure and surrounding tissue.

There are very few diseases that might involve pencil-in-cup deformity. If you don’t have skin symptoms of psoriasis, your doctor will likely check for blood markers of rheumatoid arthritis and other diseases that can cause this disorder.

PsA is often misdiagnosed. But a misdiagnosis of pencil-in-cup deformity is unlikely, because of its distinct X-ray image. Your other symptoms will guide the doctor in reaching a diagnosis of the underlying disease.

The aim of treatment for pencil-in-cup deformity is to:

  • prevent any further bone deterioration
  • provide pain relief
  • provide physical and occupational therapy to maintain the functioning of your hands and feet

Specific treatment will depend on the severity of your deformity and on the underlying cause.

For PsA-related pencil-in-cup deformity, your doctor may prescribe nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve symptoms. But these drugs won’t stop bone destruction.

To slow or stop bone loss, the doctor may prescribe disease-modifying antirheumatic drugs (DMARDs) or oral small molecules (OSMs) such as:

  • methotrexate
  • tofacitinib (Xeljanz)
  • apremilast (Otezla)

A group of drugs called biologics inhibit tumor necrosis factor (TNF-alpha), which plays a role in PsA. Examples include:

Biologics that block interleukin 17 (IL-17), which promotes inflammation, include:

  • secukinumab (Cosentyx)
  • ixekizumab (Taltz)
  • brodalumab (Siliq)

Other biologics your doctor may prescribe include:

  • ustekinumab (Stelara), which blocks the inflammatory molecules IL-23 and IL-12
  • abatacept (CTLA4-Ig), which blocks activation of T cells, a type of cell important to immune system response

Combination treatments might be needed in the most severe cases. Even more drugs are under development or in clinical trials that target the particular cells or their products thought to cause inflammation and bone destruction.

Physical and occupational therapy can be helpful for symptom relief, maintaining flexibility, reducing stress on hands and feet, and protecting joints from injury.

Discuss with your doctor what combination of treatments might be best for you. Also ask whether a clinical trial may be an option. Be sure to discuss the side effects of DMARDs, oral small molecules (OSMs), and biologics. Also consider cost, because some of the newer drugs are very expensive.

In some cases, reconstructive surgery or joint replacement may be an option.

Surgery for PsA isn’t common: One study found that only 7 percent of people with PsA had orthopedic surgery. A 2008 review of PsA and surgery noted that surgery in some cases successfully relieved pain and improved physical function.

Pencil-in-cup deformity can’t be cured. But many available drug treatments can slow or stop further bone deterioration. And even more promising new drugs are under development.

Physical therapy can help in strengthening muscles and keeping your joints, hands, and feet flexible and functional. An occupational therapist may be able to help with appliances to aid in mobility and performing daily tasks.

Eating a healthy anti-inflammatory diet and getting regular exercise can help your overall health.

Starting counseling or joining a support group may help you cope with stress and disability. The Arthritis Foundation and the National Psoriasis Foundation both provide free help.