In the first place, the physician diagnoses pseudogout when X-rays show the typical calcification of joint surfaces (articular cartilage) due to shedding of pyrophosphate crystals. Certainly, this is called “chondrocalcinosis“. On this image the menisci between the thigh bone and the tibial bone show spurs of calcification.
Samples under the polarized light microscope show the rhomboid, square or rod-shaped crystals, which makes the diagnosis. To emphasize, the laboratory physician obtains such samples either from centrifuged synovial fluid samples, from direct biopsies and often from white blood cells of the inflamed tissue around joints.
Surely, iron storage disease (hemochromatosis) can trigger pseudogout. Therefore, a serum ferritin level would be desirable, if hemochromatosis is clinically suspected.
Again, other tests might include a TSH test to rule out hypothyroidism. Occasionally the physician will order a parathyroid hormone test, if there is an elevated serum calcium level and there is suspicion of a parathyroid adenoma. For example, in the case of clinical evidence of amyloidosis the specialist might consider the following. Notably, the physician will do a rectal biopsy or a subcutaneous fat pad aspiration. Specifically, the laboratory physician does special staining tests and examination under a polarizing microscope to detect the characteristics of amyloid. To summarize, at the end between the blood tests, the X-rays and a possible biopsy the diagnosis of pseudogout can be made.
References
1. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 55.
2. ABC of rheumatology, second edition, edited by Michael L. Snaith , M.D., BMJ Books, 1999.
3. Goldman: Cecil Textbook of Medicine, 21st ed.(©2000)W.B.Saunders
4. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.
5. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier
