Non-neoplastic bone, joint, and soft tissue pathology: What every pathologist should know

The diagnosis of bone and soft tissue tumors is a skill which requires experience across multiple disciplines while their incidence is small. By contrast, the numbers of patients with non-tumorous diseases of bones, soft tissues, and joints dwarfs primary tumors by several orders of magnitude. The ability to successfully diagnose non-neoplastic diseases requires a knowledge of bone development, structure, remodeling, imaging, and tissue processing. This review summarizes the alterations of bones, joints, and to a lesser extent soft tissues that are encountered in the practice of everyday surgical pathology.

Inflammatory disorders mimicking periprosthetic joint infections may result in false-positive α-defensin

OBJECTIVES

The antimicrobial peptide α-defensin has recently been introduced as a potential 'single' biomarker with a high sensitivity and specificity for the preoperative diagnosis of periprosthetic joint infections (PJIs). However, most studies assessed the benefits of the test with exclusion of patients with rheumatic diseases. We aimed to evaluate the α-defensin test in a cohort study without exclusion of people with inflammatory diseases.

METHODS

Between June 2016 and June 2017, we prospectively included cases with a suspected PJI and an available lateral flow test α-defensin (Synovasure^®) in synovial fluid. We compared the test result to the diagnostic criteria for PJIs published by an International Consensus Group in 2013.

RESULTS

We included 109 cases (49 hips, 60 knees) in which preoperative α-defensin tests had been performed. Among these, 20 PJIs (16 hips, four knees) were diagnosed. Preoperative α-defensin tests were positive in 25 cases (22.9%) with a test sensitivity and specificity of 90% and 92.1% (95% CI 68.3%-98.8% and 84.5%-96.8%, respectively), and a high negative predictive value of 97.6% (95% CI 91.7%-99.4%). We interpreted seven α-defensin tests as false positive, mainly in cases with inflammatory rheumatic diseases, including crystal deposition diseases.

CONCLUSIONS

A negative synovial α-defensin test can reliably rule out a PJI. However, the test can be false positive in conjunction with an underlying non-infectious inflammatory disease. We therefore propose to use the α-defensin test only in combination with Musculoskeletal Infection Society criteria and assessment for crystals in synovial aspirates.

Intra-articular basic calcium phosphate and monosodium urate crystals inhibit anti-osteoclastogenic cytokine signalling

OBJECTIVE

Basic calcium phosphate (BCP) and monosodium urate (MSU) crystals are particulates with potent pro-inflammatory effects, associated with osteoarthritis (OA) and gout, respectively. Bone erosion, due to increased osteoclastogenesis, is a hallmark of both arthropathies and results in severe joint destruction. The aim of this study was to investigate the effect of these endogenous particulates on anti-osteoclastogenic cytokine signalling.

METHODS

Human osteoclast precursors (OcP) were treated with BCP and MSU crystals prior to stimulation with Interleukin (IL-6) or Interferon (IFN-γ) and the effect on Signal Transducer and Activator of Transcription (STAT)-3 and STAT-1 activation in addition to Mitogen Activated Protein Kinase (MAPK) activation was examined by immunoblotting. Crystal-induced suppressor of cytokine signalling (SOCS) protein and SH-2 containing tyrosine phosphatase (SHP) expression was assessed by real-time polymerase chain reaction (PCR) in the presence and absence of MAPK inhibitors.

RESULTS

Pre-treatment with BCP or MSU crystals for 1 h inhibited IL-6-induced STAT-3 activation in human OcP, while pre-treatment for 3 h inhibited IFN-γ-induced STAT-1 activation. Both crystals activated p38 and extracellular signal-regulated (ERK) MAPKs with BCP crystals also activating c-Jun N-terminal kinase (JNK). Inhibition of p38 counteracted the inhibitory effect of BCP and MSU crystals and restored STAT-3 phosphorylation. In contrast, STAT-1 phosphorylation was not restored by MAPK inhibition. Finally, both crystals potently induced the expression of SOCS-3 in a MAPK dependent manner, while BCP crystals also induced expression of SHP-1 and SHP-2.

CONCLUSION

This study provides further insight into the pathogenic effects of endogenous particulates in joint arthropathies and demonstrates how they may contribute to bone erosion via the inhibition of anti-osteoclastogenic cytokine signalling. Potential targets to overcome these effects include p38 MAPK, SOCS-3 and SHP phosphatases.

Calcium hydroxyapatite crystal deposition with intraosseous penetration involving the posterior aspect of the cervical spine: a previously unreported cause of neck pain

PURPOSE

Calcific tendinitis is a frequent disorder caused by hydroxyapatite crystal deposition; however, bone erosions from calcific tendinitis are unusual. The spinal manifestation of this disease is calcific tendinitis of the longus colli muscle; this disease has never been described in the posterior aspect of the spine. We report a case of calcium hydroxyapatite crystal deposition involving the posterior cervical spine eroding the bone cortex.

METHODS

A 57-year-old woman presented with a 5-month history of left-sided neck pain. Radiographs showed C4-C5 interspinous calcification with lytic compromise of the posterior arch of C4. Magnetic resonance imaging confirmed a lytic lesion of the posterior arch of C4, with a soft tissue mass extending to the C4-C5 interspinous space; calcifications were observed as very low signal intensity areas on T1 and T2 sequences, surrounded by gadolinium-enhanced soft tissues. A computed tomography (CT) scan confirmed the bone erosions and the soft tissue calcifications.

RESULTS

A CT-guided needle biopsy was performed; it showed vascularized connective tissue with inflammatory histiocytic infiltration and multinucleated giant cells; Alizarin Red stain confirmed the presence of hydroxyapatite crystals. The patient was treated with anti-inflammatories for 2 weeks. She has been asymptomatic in a 6-month follow-up; a CT scan at the last follow-up revealed reparative remodeling of bone erosions.

CONCLUSION

This is the first report of calcium hydroxyapatite crystal deposition with intraosseous penetration involving the posterior aspect of the cervical spine. Considering that this unusual lesion can be misinterpreted as a tumor or infection, high suspicion is required to avoid unnecessary surgical procedures.

Bilateral Olecranon Bursitis - A Rare Clinical presentation of Calcium Pyrophosphate Crystal Deposition Disease

INTRODUCTION

Calcium pyrophosphate crystal deposition disease (CPPD) is the most common form of crystal arthropathy second only to gout. Common clinical presentation is an acute monoarticular arthritis commonly occurring in knee joints. We presented a case of bilateral olecranon bursitis in a calcium pyrophosphate crystal deposition disease.

CASE REPORT

A 42-year-old female patient is presented with golf ball sized painless swellings in the posterior aspect of her elbows. Elbow joints were clinically normal except for restriction of terminal flexion. X-ray showed mild erosion at the tip of olecranon. Excision biopsy of the swelling showed positive birefringent calcium pyrophosphate dehydrate crystals on the inner wall of the specimen on polarized light microscopy.

CONCLUSION

Bilateral olecranon bursitis may be part of the extraarticular manifestations of calcium pyrophosphate dihydrate crystal deposition disease with good prognosis following in toto bursa excision.