Calcium-containing crystal arthritis

As we age or with certain metabolic conditions calcium-containing deposits (crystals) can accumulate in our bodies. Often these cause no problems. Indeed, if we did an X-Ray on many people in their 80s we would see calcium in the soft-tissues. Some people are more prone to get calcium-containing deposits in their tissues. The different crystals that form from these deposits include basic calcium-phosphate crystals (BCPs), hydroxyapatite (HA) and calcium pyrophosphate (CPP). Under certain situations - often following another illness - these crystals can be 'unmasked' to the body's immune system which then mounts an 'attack' giving rise to either acute, or sometimes chronic inflammation and symptoms pain and swelling in or around joints, neck and spine. 

The most easily identified calcium-containing crystals are CPP crystals (CPP disease). These crystals can cause acute inflammation or pain/stiffness or chronic arthritis typically at the following sites: joints, a whole hand or foot, the spine and the top of the neck (odontoid bone). CPP disease is highly varied in its effects and because it can affect many different musculoskeletal structures in the body, not just joints, its sometimes referred to as calcium pyrophosphate deposition disease (CPPD).

One form of CPPD is termed 'pseudogout'. This is because it is very similar to acute gout in causing an acute attack of pain and swelling in a joint. Joints or a foot or hand can suddenly swell, be stiff and painful - just like gout. The diagnosis of pseudogout is made on polarised light microscopy examination of fluid taken from an inflamed joint (and this test discriminates from gout).

CPPD can often mimic (or better considered - is one cause of) polymyalgia rheumatica. Some underlying metabolic conditions increase the risk of having CPPD include: Kidney Diseases, Hyperparathyroidism, Hemochromatosis, hypomagnesemia, hypophosphatasia, but most people with CPPD don’t have these other conditions.

Treatment depends on where the inflammation is and how bad it is. Usually anti-inflammatory painkillers (NSAIDs) and a time-limited course of steroid tablets are used for the acute form of the disease - pseudogout. Chronic CPPD can respond to methotrexate and sometimes hydroxychloroquine in certain cases.
 

Links

Patient information on pseudogout at ‘Versus Arthritis’ UK medical charity website:
https://www.versusarthritis.org/about-arthritis/