Pseudogout or calcium pyrophosphate dihydrate deposition disease (CPPD) primarily affects the joints and the periarticular tissues. Tophaceous or tumoral pseudogout is a rare form of this disease which is seen around the joints of extremities. It can be misdiagnosed as a neoplastic condition because of its clinicoradiological similarities, and thus, a proper histopathological examination is indispensable. We report one such case of extra-articular deposition of the CPPD crystals in a 65-year-old man who presented with an asymptomatic swelling around the left ankle. Radiographs showed a dense homogenous calcification, and FNAC revealed dense calcium deposits with numerous rhomboid-shaped crystals. It was managed by en bloc excision, and postoperative biopsy reports confirmed the diagnosis. Possibility of pseudogout should be kept as a differential diagnosis in patients presenting with calcified soft tissue swellings and should be subjected to a detailed histopathological examination for confirmation.
Pseudogout or calcium pyrophosphate dihydrate deposition disease (CPPD) is characterized by accumulation of calcium pyrophosphate dihydrate crystals in the intra-articular and periarticular tissues [
A 65-year-old man presented to the orthopaedic outpatient department with the chief complaint of swelling over the lateral aspect of his left ankle for the past two years. There was no history of any preceding trauma. The swelling did not increase in size and was not associated with any pain. On clinical examination, there was a
Swelling of
Anteroposterior X-ray of the left ankle joint showing a radiopaque mass with dense homogenous calcification over the lateral aspect of the ankle joint.
Considering the benign nature of the condition, a FNAC was done, and smears showed dense deposits of calcium with numerous refractile radiating rhomboid-shaped crystals which were seen against amorphous material (Figure
FNAC (Pap stain ×40) showing foci of calcium deposits with numerous highly refractile rhomboid-shaped crystals.
Ovoid-shaped mass measuring
Biopsy: (a) (H&E stain ×200) large globular deposits of calcium with rhomboid-shaped crystals surrounded by mild inflammatory reaction; (b) (H&E stain ×400) CPPD crystals along with minimal lymphocytic infiltration and foci of calcification.
Calcium pyrophosphate dihydrate deposition disease (CPPD) is the most common form of crystal arthropathy second only to gout. It commonly presents as a monoarticular arthritis with crystal deposition in the synovial membranes, menisci, joint cartilages, and periarticular soft tissues. The knee is the most frequently involved joint followed by the wrist, shoulder, ankle, and elbow [
It manifests as a soft tissue swelling forming a tumor-like mass due to deposition of the CPPD crystals [
Typically, a case of pseudogout appears as a soft tissue mass of varying internal calcification often associated with erosion of adjacent bones [
A wide variety of conditions can simulate tophaceous pseudogout which include inflammatory conditions like tophaceous gout, myositis ossificans, benign conditions such as tumoral calcinosis, synovial chondromatosis, calcified lipoma, and BPOP, and malignant tumors such as synovial sarcoma, pleomorphic undifferentiated sarcoma, chondrosarcoma, and parosteal osteosarcoma [
Differential diagnosis for the patient in our case report and their distinguishing features.
Site of origin | Most common distribution | Radiological appearance | Histological appearance | |
---|---|---|---|---|
Tumoral pseudogout | Periarticular | Temporomandibular joint, perispinal tissues, joints of extremities | Radiopaque soft tissue mass with varying densities of calcification | Amorphous calcium deposits with numerous refractile radiating rhomboid crystals, demonstrates positive birefringence on polarized microscopy |
Tophaceous gout | Periarticular | 1st MTP joint, hands and feet | Juxtaarticular punched out erosions with sclerotic margins | Tophi—granulomatous inflammation with plenty of needle-shaped crystals. Negative birefringence on polarized microscopy |
Tumoral calcinosis | Periarticular | Around large joints like the hip, shoulder, and elbow | Amorphous multilobulated (cloud-like) appearance | Lobules of calcific material surrounded by histiocytic giant cells |
Synovial chondromatosis | Mainly intra-articular, sometimes in bursal tissues and tendon sheaths | Knee joint (70%), hip, shoulder, elbow | Calcified loose bodies in the joint, ring and arc appearances | Cartilage cells with varying degrees of atypia. Varying degrees of calcification and ossification |
Myositis ossificans | Large muscle groups of the extremities | Around the knee, hip, and elbow | Circumscribed calcification with a lucent centre | Inner cellular zone, middle zone of woven bone, outer zone of mineralized bone |
BPOP | Bony surfaces | Distal extremities, hands and feet | Continuous with the cortex with an underlying intact cortex | Chondro-osteoid matrix containing enlarged, bizarre, binucleated chondrocytes |
Lipoma | Typically present in the subcutaneous plane | Usually found over the back, shoulders, and neck region but can be seen in other locations also | Calcifications are seen in 11% of the cases. |
Well-circumscribed encapsulated mass of mature adipocytes. Deeper lipomas may be associated with malignant features |
Synovial sarcoma | Soft tissues of the body. In the extremities seen adjacent to large joints | Extremities, trunk, intrathoracic or intra-abdominal | Nonspecific calcification pattern | Biphasic or monophasic forms. Focal calcifications seen in 1/3rd of the cases |
Chondrosarcoma | Long bones | Femur, pelvis | Ring and arc (popcorn) types of calcifications | Focal calcifications with no osteoid or bone formation |
Parosteal osteosarcoma | Metaphysis of long bones | Distal femur, proximal humerus, proximal tibia | Large lobulated exophytic mass, usually circumferential involvement, central dense ossification; string sign—radiolucent line separating the tumor from the cortex | Low grade tumor. Well-formed bony trabeculae and osteoid deposition with or without osteoblastic rimming; stromal cells show mild cellular atypia and few mitoses |
A case of tophaceous pseudogout involving the ankle joint has been previously reported by Seybold et al. [
Therefore, to conclude, although a good histopathological study is indispensable for the diagnosis of this relatively rare disease in view of its clinicoradiological similarities with other diseases, the best approach would be a systematic one considering the clinical radiological and histological features in toto to obviate the need for repeated surgical interventions.
The present report is unique in itself in describing such a huge swelling of tumoral CPPD around the ankle joint without any bony destruction and an atypical radiological presentation. Demonstration of calcium phosphate dihydrate crystals in the calcified deposits helps us in differentiating it from benign or malignant calcifications. A holistic approach considering the clinical, radiological, and histological features is needed for appropriate management and outcomes.
Informed consent was obtained from the patient.
The authors declare that there is no conflict of interest regarding the publication of this paper.