Hypertrophic osteoarthropathy (HOA) is a condition that affects your joints and bones. It combines the following main features in the hands and feet:

HOA can be primary (occurring alone) or secondary to certain conditions like lung cancer. While primary HOA is a rare genetic disorder, secondary HOA is a more common alarming sign of several health conditions that should prompt you to speak with a doctor.

Read on to learn about HOA, including its symptoms, what it looks like (with photos), when to seek medical advice, and how it’s treated.

The hallmark triad of HOA symptoms includes:

Clubbing is usually the first sign of this condition with periostosis and arthralgia appearing as the condition progresses.

Clubbing can involve your fingers and toes. Symptoms usually include:

  • enlarging or bulging of the tip of your fingers or toes
  • disappearing of the angle between your nails and cuticle
  • downward curving of your nails
  • softening of the nail beds
  • nails having an appearance of floating instead of being firmly attached to your fingers or toes
  • redness and warmth in the nails and nail beds
  • the skin at the base of the nail looking shiny and thin

Other symptoms of HOA may include:

  • thickening of your skin
  • synovial effusions (excess of synovial liquid in your joints)

Let’s look at how HOA may present on hands and feet.

HOA has two types: primary and secondary. It’s important to know the differences between these conditions because of different treatment approaches.

Primary HOA

Primary HOA is also known as pachydermoperiostosis (PDP). It’s a rare genetic disorder that can run in some families.

In addition to the typical triad of HOA symptoms, PDP can cause:

Symptoms of primary HOA usually become apparent in childhood.

Secondary HOA

Secondary HOA appears due to certain underlying medical conditions. Unlike primary HOA, it typically develops in adults rather than children. The underlying condition usually appears first, although in some cases, symptoms of HOA may show up before the symptoms of the underlying condition.

Secondary HOA is much more common than primary. Researchers estimate that it comprises 95% to 97% of all HOA cases.

The causes of HOA depend on its type.

A genetic mutation in either of the two genes called HPGD and SLCO2A1 causes primary HOA. The condition can run in some families, especially if parents are closely related by blood.

The exact causes of secondary HOA aren’t yet known. But some researchers believe that hormonal changes due to certain medical conditions may be the cause.

So what are the conditions that can cause secondary HOA? While there are a few, lung cancer is the most common reason for HOA symptoms.

Lung cancer develops when your lung cells start growing out of control. The type of lung cancer most often associated with HOA is called adenocarcinoma.

Researchers believe that lung adenocarcinoma and other cancers can increase the level of growth factors in your blood. This can trigger bone, nail, and skin growth resulting in HOA symptoms.

Other lung conditions that can trigger secondary HOA include:

Less commonly, certain heart and gastrointestinal conditions can also cause HOA symptoms.

HOA itself doesn’t typically cause seriously adverse effects in the body, but potential complications of HOA include:

The underlying condition that caused your HOA may cause other complications.

If you or your child develops one of the symptoms of HOA, especially clubbing of the fingers or toes, be sure to speak with a doctor.

If you’ve been diagnosed with primary HOA or it runs in your family, you may want to speak with a genetic counselor before planning to have a baby. They can help you estimate the likelihood of passing this condition on to your children.

To diagnose HOA, a doctor will perform a careful examination of your hands and feet to confirm or rule out clubbing.

A simple test called the Schamroth sign test can be done at home to confirm clubbing. Flex the fingers of both hands.

Bring the index fingers together with nails facing each other until the distal phalanges (sections of your fingers that have nails) are touching. A diamond-shaped space appearing between your nails is called Schamroth’s window. The presence of Schamroth’s window means that your nails are not clubbed.

Once HOA is confirmed, your doctor will order additional tests to rule out any underlying conditions, particularly lung cancer.

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If you can see a diamond-shaped window of light between your pressed nails, this means you do not have clubbing. Jason Hoffman.

If the underlying cause of your HOA is established, your doctor will focus on treating the condition. For example, removal of an underlying tumor usually improves HOA symptoms.

If, after ordering tests, your doctor rules out an underlying cause, they will begin symptomatic treatment. This includes different medications, the most common of which are:

The success of treatment depends on whether the cause of HOA is identified and targeted.

Targeting and treating the underlying condition can result in quick and dramatic improvement. If the cause of secondary HOA cannot be targeted, symptoms may become more severe even with symptomatic treatment.

Primary HOA often stops progressing after your child reaches adulthood and can even resolve on its own.

The symptoms of HOA can make you uncomfortable and can be challenging to cope with.

Your doctors and nurses will do their best to make sure you receive prompt and effective treatment and that you’re as comfortable as possible.

HOA is a condition that affects your bones and joints. While it can appear on its own due to a genetic disorder, most often it’s associated with an underlying medical condition like lung cancer.

Symptoms of HOA include clubbed fingers and toes, inflammation of joints, and pain.

It’s important that you speak with a doctor if you develop clubbing or other symptoms of HOA as this can be a sign of an underlying condition. Prompt treatment of the underlying condition can dramatically improve your symptoms.