A case of Tophaceous Pseudogout: A Rare Crystalopathy Particularly Afflicting the Temporomandibular Joint

Abstract

<h3>Introduction</h3> Tophaceous pseudogout is a rare variant of CPPD crystal deposition disease presenting with a soft- tissue calcified mass. Temporomandibular joint is a common site of involvement of tophaceous pseudogout. Mu- tations in gene ANKH (inorganic phosphate transport regulator) are involved in crystal related inflammatory reac- tions. <h3>Materials and Methods</h3> We report a case of Tophaceous CPPD crystal deposition disease. A 77-year old female with no pertinent past medical or drug history, presented with persistent dull pain in her left TMJ and gradual change in occlusion over two years with intermittent trismus. Clinical examination revealed a left pre-auricular swelling with compression of the left EAC. CT imaging showed a radiopaque expansile mass encompassing the left TMJ. Surgical removal was performed together with alloplastic reconstruction using a TMJ Concepts Total Joint Replacement prosthesis. <h3>Results</h3> Microscopic examination revealed a low-grade cartilaginous proliferation with intensely basophilic calcified crys- tal deposits which were rhomboidal in appearance and polarized weakly. Few areas showed atypical, occasional binucleated chondrocytes interpreted as chondroid metaplasia. No significant bone or soft tissue invasion was identified. The clinical, histological and radiographic findings were consistent with tophaceous pseudogout (mas- sive CPPD deposition with cartilaginous metaplasia). Post-operatively the patient was pain-free with normalized occlusion and function. <h3>Conclusions</h3> Distinction from other benign chondroid neoplasms such as osteochondroma, synovial chondromatosis which may mimic CPPD disease is important. Low grade chondrosarcoma should be excluded, especially in decalcified sec- tions from which the CPPD crystals may be lost leaving behind only the atypical features in metaplastic chondro- cytes. Tophi of gout needs to be discriminated too, where monosodium urate crystals are more needle shaped and negatively birefringent under polarized light microscopy, besides hydroxyapatite crystals which appear as non- birefringent clumps. Correct identification of the type of crystal deposition is paramount to the treatment of crystal arthropathy as the underlying metabolic disturbances may be quite specific.