The question “What’s in a name?” can be especially hard to answer when it comes to diseases that go by or are related to multiple names. Do these different names matter? What do they tell you?

Pediatric granulomatous arthritis (PGA) is a disease that comes with multiple names attached to it. Three of these names are Blau syndrome (BS), early-onset sarcoidosis (EOS), and chronic granulomatous disease (CGD).

Don’t worry if you’ve never heard of BS, EOS, or CGD before. You’re not alone! After all, BS is so rare that fewer than 300 people in the United States are estimated to have this condition.

In order to understand PGA, it’s essential to understand what the terms “BS,” “EOS,” and “CGD” mean. So, we’ve combed the scientific research to help you understand these names, how they fit together, and what they mean for the diagnosis and treatment of PGA.

As the name implies, PGA is arthritis that occurs in young people as a result of granulomatous inflammation.

BS, EOS, and CGD are chronic genetic disorders that cause children to experience granulomatous inflammation. So, when arthritis is present as a result of this granulomatous inflammation, it may be referred to as PGA.

If you’re feeling confused, don’t worry — you’re not alone! It may help to know that “PGA” is an appropriate term to use anytime a child has arthritis due to granulomatous inflammation, no matter the specific underlying cause.

The path to PGA can begin with a genetic mutation. The mutation and its resulting effects are referred to as BS or EOS. BS and EOS are chronic, progressive diseases.

BS and EOS are essentially identical conditions because they have the same genetic cause and symptoms. Both include mutations to the NOD2 gene and typically display as granulomatous dermatitis (inflamed skin), arthritis (joint pain), and uveitis (swelling of the middle layer of the eye).

The difference between these two conditions is that EOS is caused by new genetic changes. It occurs in people with no history of the disorder in their family. On the other hand, BS is an inherited condition that comes with a family history of the genetic mutation.

For a person to be included in the international registry of these conditions, they need to have granulomatous inflammation, arthritis, and uveitis or an ocular rash.

Like BS and EOS, CGD is a disorder in which people can develop granulomas.

CGD is a rare, inherited immune system disorder that doesn’t allow the phagocytic leukocytes — a type of white blood cells that help prevent infections — to kill germs. This means that people with CGD don’t have protection from bacterial and fungal infections.

Children with CGD are generally born healthy but develop severe infections during infancy and early childhood. These infections can affect the lungs, skin, liver, lymph nodes, and intestines.

Individuals with CGD can also develop granulomas, which are masses of inflammatory material. These frequently grow in the skin, gastrointestinal tract, and genitourinary tract. (GCD was named for these granulomas before the genetic part of the condition was discovered.)

Most children with CGD will be diagnosed by 5 years old. Symptoms leading to this diagnosis can include:

  • fevers
  • skin rashes, which can appear as early as 1 month of age and usually appear on the face before spreading to the trunk
  • joint pain, which can be accompanied by cyst-like areas of swelling on the backs of feet and wrists
  • arthritis
  • pneumonia
  • bacterial and fungal infections

After considering an individual’s medical history and performing a physical exam, healthcare professionals frequently diagnose CGD through a skin biopsy and a variety of tests.

These can include:

  • neutrophil function tests to determine how white blood cells are functioning
  • a dihydroergotamine reduction test
  • genetic testing to confirm the specific gene mutation

It’s also important to rule out chronic infections before diagnosing someone with CGD.

The only way a healthcare professional can diagnose BS or EOS without question is by doing a genetic test for the specific NOD2 gene mutation.

Treating PGA requires a multi-disciplined approach.

Healthcare professionals often prescribe steroid medications to help manage inflammation and arthritis pain. However, prolonged use of these drugs may cause undesirable side effects.

To suppress disease activity and allow for tapering off these treatments, a healthcare professional may prescribe the immunosuppressive drug methotrexate.

There has been a lack of evidence-based therapeutic options, but healthcare professionals are beginning to use anti-TNF monoclonal antibody agents in PGA treatment. Because tumor necrosis factor (TNF)-alpha has a possible role in CGD inflammatory conditions, etanercept (an anti-TNF agent) may be a game-changer in future treatment plans.

PGA is a rare condition that causes very young children to experience arthritis pain as a result of granulomatous inflammation. Genetic disorders cause PGA. Most individuals with PGA appear healthy at birth but begin to experience skin conditions and frequent illnesses soon after birth.

PGA is very rare. If you believe your child may have PGA, the next step is to reach out to a healthcare professional for assistance and referrals.