What Is Pencil-in-Cup Deformity?

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Pencil-in-cup is a rare type of deformity associated with arthritis mutilans (AM), a severe form of psoriatic arthritis (PsA). The term “pencil-in-cup” is used to describe what the affected bone looks like on an X-ray. The appearance is similar to that of a bone having worn away and now resembling a sharpened pencil that is facing a bone that also has worn away and is now in the shape of a cup.

This deformity results in erosion of joints and bones in the hands and feet as a result of severe inflammation related to PsA. A pencil-in-cup deformity can cause movement and joint function problems.

If imaging shows signs of a pencil-in-cup deformity, it is important you start treatment right away to prevent further damage, which can happen pretty quickly.

hand X-rays

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Pencil-in-Cup Deformity Symptoms

A pencil-in-cup deformity results from osteolysis (progressive bone destruction) related to AM. Joint erosion and bone destruction from AM usually occur in the hands and feet.

Pencil-in-cup deformities lead to joint deformities and the inability to move affected joints. Because they typically form in the hands and feet, pencil-in-cup deformities can affect the way you walk and your ability to use your hands.

A pencil-in-cup deformity may involve the telescoping of affected fingers or toes. Telescoping means that the bones have dissolved so much that it appears that one part of a bone has slid into another part, like the sections of a telescope.

Pencil-in-cup, telescoping, or both can keep you from moving your affected digits or making a fist. They can also make it harder to do everyday activities, including self-care.

Arthritis mutilans—the cause of pencil-in-cup deformities—leads to severe joint pain and swelling of the hands and feet. It can also cause the bones of the hands and feet to fuse.

AM is also linked to skin lesions, which appear before damaging arthritis occurs. Some people with AM may have nail changes, including nail thickening, separation, and discoloration.

Causes

Psoriatic AM is the most severe and rare form of PsA. It affects only 5% of people with psoriatic arthritis. There are no prevalence studies on pencil-in-cup deformities, but available research shows this type of deformity is generally present in the feet in the first decade of having AM associated with PsA.

PsA is an autoimmune disease that results from the immune system attacking healthy tissues. These attacks cause inflammation that damages bones and joints. That process is triggered by numerous factors, including genes and environmental factors.

Experts believe the main cause of PsA is a combination of genetic and environmental factors. Genetic research shows that people with PsA who have two specific genes—HLA-B27 and DQB1*02—have an increased risk of developing arthritis mutilans.

Similar changes to pencil-in-cup deformities can be seen in a type of inflammatory arthritis called rheumatoid arthritis (RA). RA mainly affects the joints, usually multiple joints at once on both sides of the body.

Unfortunately, the research on arthritis mutilans in RA is limited and outdated. One 2008 report shows AM affects around 4.4% of people living with long-standing or untreated RA.

A 2013 article published in the Journal of Rheumatology reports that AM has been linked to many other conditions, including systemic lupus erythematosus (lupus), systemic sclerosis (scleroderma), juvenile idiopathic arthritis (JIA), multicentric reticulohistiocytosis (MRH), and cutaneous T cell lymphoma (a cancer that starts in the white blood cells called T cells).

Diagnosis

Arthritis mutilans is diagnosed by determining what type of inflammatory arthritis is causing it. A rheumatologist will check the joints for swelling and tenderness. They will also do blood work to determine the source of the AM.

X-rays can help your doctor to see what exactly is happening in your joints and whether the source of your joint damage is AM. Ultrasound and magnetic resonance imaging (MRI) can also confirm a diagnosis of pencil-in-cup deformity and look for the severity of any type of bone destruction.

Ultrasound scans can detect inflammation where there are no symptoms and where severe joint damage has not yet occurred. MRI scans can give your doctor a more detailed picture of small changes in bone structures and surrounding tissues.

According to a 2015 review of psoriatic AM, doctors usually look for bone and joint destruction as a diagnostic marker for AM. They will also look for telescoping and shortening of fingers and toes.

Few inflammatory joint conditions lead to pencil-in-cup deformity, and PsA is the most commonly associated with this type of damage. However, if your medical team rules out psoriatic arthritis, they will want to look for markers of rheumatoid arthritis and other inflammatory arthritis conditions linked to pencil-in-cup deformities.

Pencil-in-cup deformities are common in cases where PsA is either undiagnosed or misdiagnosed. However, a misdiagnosis of a pencil-in-cup deformity is uncommon because of distinct X-ray imaging. Additional symptoms seen in AM and PsA can also help your doctor make a diagnosis.

Treatment

Arthritis mutilans is a progressive condition. So, the sooner you're diagnosed, the better chance you have of avoiding future joint damage.

Early treatment is vital to prevent bone loss associated with AM. Bone tissue loss cannot be reversed, but treating AM can slow down any future destruction. Early treatment may also help to preserve the function of your fingers and toes.

The goals of treating pencil-in-cup deformities are to prevent further bone damage, provide pain relief, and maintain function in your hands and feet. Your treatment options might include medicines, physical therapy and occupational therapy, and surgery.

Medicines

Your doctor may prescribe several different medicines for treating pencil-in-cup deformities that have resulted from PsA. These may be given alone or together:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs): NSAIDs like ibuprofen can relieve or reduce pain and inflammation in affected joints.
  • Corticosteroids: Available as injections and oral medicines, corticosteroids work to reduce swelling and pain in your joints by suppressing your body’s overactive immune response.
  • Disease-modifying antirheumatic drugs (DMARDs): These drugs suppress the immune system’s overactive response on a broad scale and are available as both pills and injections. An example of a DMARD is methotrexate. It is often used in combination with other DMARDs to relieve symptoms of PsA and prevent long-term joint damage.
  • Biologics: Biologics are a different type of DMARD that work by interrupting certain inflammatory chemicals. They are available as injections and infusions. Examples of biologic DMARDs approved for treating PsA include Cimzia (certolizumab pegol), Cosentyx (secukinumab), and Taltz (ixekizumab).

By reducing inflammation in joints affected by pencil-in-cup deformities and the inflammatory processes that lead to joint deformities, the likelihood of further damage from PsA can be reduced. Treatment with medications is the only way to manage inflammation and reduce the effects of an overactive immune system.

Physical and Occupational Therapy

Both physical and occupational therapy can help to relieve pain and other symptoms from pencil-in-cup deformities and keep the deformity from worsening. These therapies can also help to take the strain off your hands and feet, stop PsA from causing further damage, and keep your joints flexible and mobile.

Surgery

Surgery for pencil-in-cup deformities is usually a last resort. Surgical options your doctor might recommend to treat a pencil-in-cup deformity include joint fusion, joint replacement, or reconstructive surgery.

Summary

Pencil-in-cup deformity is a rare type of bone destruction seen in the fingers and toes of people with arthritis mutilans. This condition is usually associated with psoriatic arthritis. The change in bone shape can make it difficult to move the affected digits. Medications may be used to slow the destruction and relieve symptoms.

A Word From Verywell

A pencil-in-cup deformity cannot be reversed, but there are many treatment options to slow down or stop further damage. Psoriatic arthritis mutilans is not always preventable, but following your psoriatic arthritis treatment plan can keep inflammation under control and slow down the progression of PsA and psoriatic AM.

It is also possible to achieve remission from PsA with the many treatment options available for the condition. Remission means the condition is inactive, or a person is experiencing low disease activity. 

Remission might reduce your risk for AM or joint damage from PsA. Even with remission, you will still need to stay on top of your treatment plan to keep the disease from worsening and the symptoms from returning.

Frequently Asked Questions

How common is arthritis mutilans?

Arthritis mutilans is a severe, rare, and extremely destructive type of arthritis. It affects about 5% of people with severe psoriatic arthritis. It is also seen with some other types of inflammatory arthritis, but it is even rarer in other conditions.

What does pencil-in-cup mean on an X-ray?

The term “pencil-in-cup” describes what is seen in imaging in a bone affected by psoriatic arthritis mutilans. X-rays from this type of destruction show damaged bone where the end of that bone has been eroded into a shape that appears pointy and sharpened like a pencil. The pencil area has worn away the surface of a nearby bone and caused it to appear cuplike.

Is pencil-in-cup deformity permanent?

Pencil-in-cup deformities are the result of arthritis mutilans. AM can cause bone loss, which leads to changes in the shape of your fingers and toes and impairs your movement. AM leads to permanent damage to your fingers, toes, hands, and feet. Pencil-in-cup deformities are also permanent, and if left to worsen, they will later require surgery to repair the damage.

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