Pencil-in-cup deformity is a rare bone and joint condition usually associated with a severe form of arthritis called arthritis mutilans. On a scan, the affected bone may seem pointed, like a sharpened pencil, and it may wear away at a nearby surface, which becomes cup-like.

Arthritis mutilans is a severe manifestation of arthritis. It is, for example, the most severe and least common form of psoriatic arthritis, developing in roughly 5% of people with the condition. It also occurs in 4.4% of people with rheumatoid arthritis.

Arthritis mutlians may also be associated with scleroderma, gout, and systemic lupus erythematosus.

Pencil-in-cup deformity results from erosion of joints and destruction of bones in the hand and feet. It can cause movement problems. If scans show any signs of pencil-in-cup deformity, it is important to receive treatment right away to prevent further degeneration, which can happen rapidly.

Below, learn more about this condition and the health issues that are most likely to cause it.

An X-ray showing a pencil-in-cup deformity.Share on Pinterest
Leung, Ying Ying, Tam, Lai-Shan, W KUN, Emily, Li, Edmund. Hong Kong Bulletin of Rheumatic Diseases.

To better understand the cause of pencil-in-cup deformity, it helps to know more about the two conditions most frequently associated with it: psoriatic arthritis and rheumatoid arthritis.

Psoriatic arthritis

Psoriatic arthritis is an autoimmune condition — it results from the immune system attacking healthy tissue. This causes inflammation that leads to joint damage. Evidence suggests that psoriatic arthritis occurs in about 30% of people with psoriasis. While experts are unsure of the cause, they believe that it may involve genetic factors and environmental triggers.

Rheumatoid arthritis

Rheumatoid arthritis is also an autoimmune condition. The Centers for Disease Control and Prevention (CDC) note that the cause is unknown, but that risk factors include genetics and environmental triggers.

Arthritis mutilans

Arthritis mutilans is a severe form of arthritis that destroys bone and cartilage within joints and causes bone resorption. This is part of the bone modeling process, which involves the breakdown and absorption of old bone tissue. However, in people with arthritis mutilans, bone tissue rebuilding does not occur. Instead, the soft tissues of the bones collapse. This can cause pencil-in-cup deformity.

The defining feature of pencil-in-cup deformity is the characteristic wearing away of bones. A doctor might describe this as severe bone tissue destruction. It typically results in joint deformity and an inability to move the joint. This issue mostly occurs in the hands, but it can also develop in the feet.

The deformity is often visible. It may involve telescoping of the affected fingers or toes. Telescoping stems from the dissolution of bones, and as a result, one part of the finger or toe “slides into” the next part, as the soft tissues that remain cannot provide enough structure. Some healthcare professionals refer to this as having “opera glass hands.”

This condition prevents a person from being able to move the affected digits well or make a fist. It can be challenging to do everyday activities, such as cooking and dressing.

To diagnose arthritis mutilans and pencil-in-cup deformity, a doctor first identifies the underlying condition, such as the type of arthritis.

If they suspect psoriatic arthritis, for example, a doctor uses a classification system developed in 2006. It includes criteria such as psoriatic skin changes, nail degeneration, finger swelling, and abnormal new bone formation. The doctor also does a physical examination and asks about family history and any current symptoms.

To confirm a diagnosis of pencil-in-cup deformity, the doctor uses multiple imaging tests, which can include:

For someone with pencil-in-cup deformity, it is important to receive treatment as soon as possible to prevent further bone loss and joint damage.

Treatments typically include medications, physical and occupational therapy, and surgery. The aim is to limit bone deterioration, relieve pain, and maintain the functioning of the hands and feet. Specific treatments depend on the severity of the deformity and the underlying cause.

For pencil-in-cup deformities resulting from psoriatic arthritis, doctors may recommend one of or a combination of the medications below:

  • Disease-modifying antirheumatic drugs (DMARDs): These suppress the immune system broadly and are available as pills or injections. They may take 3 months to take effect. An example is methotrexate (Trexall).
  • Biologics: These are a different type of DMARD. They interrupt certain chemicals involved in inflammation and are available as injections or infusions. An example is etanercept (Enbrel).
  • Nonsteroidal anti-inflammatory drugs (NSAIDs): These may help relieve or reduce pain by lowering levels of inflammation in the joint. An example of an over-the-counter NSAID is ibuprofen (Advil).
  • Corticosteroids: Corticosteroids may help reduce swelling and pain in joints by suppressing the body’s immune response.

Physical and occupational therapies can also help keep the issue from worsening, relieve symptoms, maintain flexibility, reduce strain on the hands and feet, and protect the joints from injury.

Surgery for pencil-in-cup deformity is typically a last resort. Surgical options may include joint fusion, joint replacement, or reconstructive surgery.

Psoriatic arthritis is a long-term inflammatory condition of the joints and the sites where ligaments and tendons connect to bones. The condition typically occurs in people with psoriasis, but it can develop in people without the condition, especially in people who have relatives with psoriasis.

Psoriatic arthritis usually appears in people aged 30–50 years old, but it can begin in childhood.

Learn more about psoriatic arthritis mutlians here.

Pencil-in-cup deformity usually results from a severe bone and joint condition called arthritis mutilans. It typically develops as a severe form of psoriatic or rheumatoid arthritis.

Imaging techniques help doctors diagnose this deformity. In the affected finger or toe, the bone may appear pointed, like a sharpened pencil, and it may wear away at a nearby surface, which becomes cup-like.

Early treatment can be key, and the doctor may recommend medications, physical and occupational therapy, and, as a last resort, surgery. The goal is to limit bone deterioration, relieve pain, and maintain the functioning of the hands and feet. The specific approach depends on the severity of the deformity and the underlying cause.