It is well recognised that the temporomandibular joint (TMJ) may be affected by rheumatoid or psoriatic arthritides and ankylosing spondylitis. Interestingly, however, calcium pyrophosphate dihydrate (CPPD) crystal deposition is unusual in this site, and authors of several large case series of CPPD disease failed to report any acute attacks affecting this joint.^1,2 As far as we are aware, only infrequent reports of CPPD crystal deposition in the TMJ have been published.^3–7 We therefore present the following case to highlight a possible differential diagnosis for patients presenting with TMJ pain and/or swelling.

CASE REPORT

A 57 year old man presented with an acute onset of severe pain and swelling affecting his right TMJ, on a background of chronic right sided TMJ discomfort. There were no associated systemic features. The patient had a past history of hypertension, hypercholesterolaemia, lumbar spine osteoarthritis, fifty (50) pack year smoking history, and an alcohol intake of 90 g/day. There was no previous history of gout or CPPD disease, and subsequent hand and knee x ray investigations did not demonstrate chondrocalcinosis.

Clinical examination disclosed an uncomfortable, but otherwise well appearing man, with a warm tender swelling over his right TMJ associated with pain on attempting to open the joint. Blood investigations included a normal full blood count (haemoglobin 144 g/l, platelets 229×10⁹/l, white cell count 10.5×10⁹/l), C reactive protein 33 mg/l (normal 0–6 mg/l), normal electrolytes (including urate, magnesium, phosphate, calcium, and thyroid function), mild increase of alkaline phosphatase and γ- glutamyltransferase, normal iron studies, negative rheumatoid factor, positive antinuclear antibody (1/320 homogeneous pattern), negative extractable nuclear antigens, and negative antibodies to double stranded deoxyribonucleic acid. A plain radiograph of the right TMJ showed enlargement and irregularity of the right condylar head, confirmed by a computed tomography scan. In addition, synovial swelling around the TMJ, calcified loose bodies, articular sclerosis, and erosions were demonstrated. A joint aspirate comprised a thick, straw coloured fluid, and the patient proceeded to surgical irrigation of the upper and lower compartments of the joint to exclude septic arthritis. Synovial fluid analysis showed large numbers of leucocytes (up to 5.9×10⁹/l and 70% polymorphs) and multiple weakly positive birefringent calcium pyrophosphate crystals. Gram stain and cultures were negative, thereby excluding infection.

The patient was treated with non-steroidal anti-inflammatory drugs (indometacin), with resolution of the acute inflammation. Mild restriction of movement and pain have persisted, secondary to underlying osteoarthritis, evident on magnetic resonance imaging. The patient continues to receive colchicine 0.5 mg twice daily and presently is unaffected by features of CPPD disease in the TMJ or other joints.

DISCUSSION

Recognised as a distinct disease entity in the early 1960s,⁸ CPPD deposition disease has emerged as a heterogeneous disorder, with clinical presentations ranging from an acute arthritis to chronic pain secondary to degenerative cartilage disease. Although CPPD crystal formation remains incompletely understood, it is known to be influenced by a high ionic product (calcium²⁺×inorganic pyrophosphate) and tissue promoters or inhibitors of crystal nucleation and growth.⁹ Prevalence increases with advancing age and the presence of metabolic/endocrine abnormalities, such as haemochromatosis, hypothyroidism, and hypomagnesaemia, none of which were present in our patient.

The knee is affected in over half of all acute attacks of CPPD disease,¹⁰ and as indicated by published reports, primary manifestation of CPPD arthropathy in the TMJ is relatively rare.^3,7 Current available explanations do not clarify why the TMJ is so infrequently affected despite containing a fibrocartilage disc similar to that in the knee. It has been suggested that this may relate to the lack of clinical distinction between this entity and osteoarthritis of the TMJ and the infrequent pathological examination of TMJs.³ However, these explanations appear to simply imply an oversight of the condition and do not offer a pathophysiological reasons for the infrequent involvement.

An alternative proposal suggests that the peculiar anatomy of the adult TMJ, with its absence of hyaline cartilage in comparison with other diarthrodial joints, is an important contributor.³ Although the exact reason as to why the temporomandibular joint appears to be relatively “protected” from CPPD crystal deposition remains to be elucidated, clinicians should be alert to the possibility of its occurrence in this joint. In addition, this case highlights the importance of mandatory synovial fluid analysis for crystals in any acute undiagnosed arthritis, to facilitate prompt diagnosis and appropriate treatment.