Identification of Common Pathogenic Pathways Involved in Hemochromatosis Arthritis and Calcium Pyrophosphate Deposition Disease: a Review.

OBJECTIVES: Arthritis is a common clinical manifestation of hereditary hemochromatosis (HH), and HH is one of a handful of conditions linked to calcium pyrophosphate deposition (CPPD) in joints. The connection between these two types of arthritis has not yet been fully elucidated. In light of new pathogenic pathways recently implicated in CPPD involving bone, we reviewed the literature on the etiology of hemochromatosis arthropathy (HHA) seeking shared pathogenic mechanisms. RESULTS: Clinical observations reinforce striking similarities between HHA and CPPD even in the absence of CPP crystals. They share a similar joint distribution, low grade synovial inflammation, and generalized bone loss. Excess iron damages chondrocytes and bone cells in vitro. While direct effects of iron on cartilage are not consistently seen in animal models of HH, there is decreased osteoblast alkaline phosphatase activity, and increased osteoclastogenesis. These abnormalities are also seen in CPPD. Joint repair processes may also be impaired in both CPPD and HHA. CONCLUSIONS: Possible shared pathogenic pathways relate more to bone and abnormal damage/repair mechanisms than direct damage to articular cartilage. While additional work is necessary to fully understand the pathogenesis of arthritis in HH and to firmly establish causal links with CPPD, this review provides some plausible hypotheses explaining the overlap of these two forms of arthritis.

Neutrophil extracellular traps release in gout and pseudogout depends on the number of crystals regardless of leukocyte count.

OBJECTIVES: Microcrystal-induced arthritis is still an unresolved paradigm for medicine. Overt inflammation may be absent even when crystals occur in SF. Recently, the production of neutrophil extracellular traps (NETs) embedding MSU crystals has been proposed as a possible mechanism of the auto-resolution of the inflammatory phase during gout. We aimed to verify and quantify the release of NETs in SFs during gout and pseudogout attacks and to compare any differences with respect to crystals and neutrophils number, and to analyse activation of necroptosis pathway in SF from crystal-induced arthritis. METHODS: SF samples were obtained by arthrocentesis from 22 patients presenting acute crystal-induced arthritis, gout or pseudogout (n = 11 each group), and from 10 patients with acute non-crystal arthritis as controls. NETosis was quantified in SF by nucleic acid stain and by quantification of human neutrophil elastase. Activation of phosphorylated MLKL was assessed by western blot. RESULTS: We observed that SF neutrophils encountering MSU and CPPD crystals during episodes of gout and pseudogout release NETs in relation to the number of crystals in SF and irrespective of neutrophil density and type of crystal. This release was accompanied by necroptosis through the activation of the MLKL pathway. CONCLUSIONS: Our findings suggest that a role of NETs in crystal-induced arthritis is to 'trap extracellular particles', including microcrystals. Embedding crystals in aggregates of NETs may be the basis of tophi and CPPD deposition, and may have implications for disease evolution rather than for spontaneous resolution of the acute attack.

Cartilage calcification is associated with histological degeneration of the knee joint: a highly prevalent, age-independent systemic process.

OBJECTIVES: To investigate if cartilage calcification (CC) is a systemic process, the purpose of this study was to determine the prevalence and the amount of meniscal/hyaline CC of the knee joint in the general population by high-resolution imaging (DCR) and to evaluate the association between CC with cartilage degeneration and age. METHODS: Cross-sectional DCR-study of 180 knee joints of 90 donors (42 female/48 male, mean age 62.3y). Histological hyaline (OARSI) and meniscal (Krenn) cartilage degeneration was determined of all knees. RESULTS: CC was observed in 100% of the donors (bilaterally in 98%), hyaline cartilage calcification (HCC) in 92% and meniscal calcification (MC) in 100%. CC was detected in more than three out of six distinct cartilage areas in 84.4% of all knees. The mean amount of CC correlated between both sides of donors, the different analyzed areas of the knee joint and between the various types of cartilage structures. There was more calcification in meniscal than in hyaline cartilage (factor 5.3) and in the medial than the lateral compartment (factor 1.2). HCC/MC were already detectable with only mild cartilage lesions and the amount correlated with histological cartilage degeneration, but not with age. CONCLUSIONS: The present study provides evidence that meniscal and hyaline CC occurs in a pattern that is compatible with CC being a systemically driven process and that meniscal fibrocartilage is more prone to calcification than hyaline cartilage. Furthermore, the age-independent association between the amount of CC and the grade of degeneration in both hyaline and meniscal cartilage, suggests that CC is an obligatory early event in initiating cartilage degeneration.

Fluorescence Differentiation of ATP-related Multiple Enzymatic Activities in Synovial Fluid as a Marker of Calcium Pyrophosphate Deposition Disease using Kyoto Green.

Calcium pyrophosphate deposition disease (CPPD) is a crystal induced inflammation in joints, and causes severe pain in elderly people. The accumulation of pyrophosphate (PPi) in synovial fluid (SF) results from several enzymatic reactions, especially the highly activated e-NPPs, which catalyze the conversion of ATP to PPi. This study demonstrates the detection of relative catalytic activity of 3 enzymes-ecto-nucleotide pyrophosphatase/phosphodiesterases (e-NPPs), tissue nonspecific alkaline phosphatase (TNAP), and ecto-nucleoside triphosphate diphosphohydrolases (e-NTPDases)-using a single molecular sensor called Kyoto Green. Kyoto Green exhibits excellent performance in sensing the catalytic activity of the commercial representatives of the e-NPPs, TNAP, and e-NTPDases, which are ENPP1, PPase, and apyrase, respectively, in both single-enzyme and multi-enzyme assays. Analysis of SF enzymes in 19 SF samples from human and swine revealed moderate activity of e-NPPs, high activity of e-NTPDases, and low activity of TNAP. Our newly developed method for analysis of multiple enzymatic activities using Kyoto Green in biological SF will assist improvement in accuracy of the CPPD prognosis/diagnosis, which will minimize unnecessary medical procedures.

Most needle-shaped calcium pyrophosphate crystals lack birefringence.

OBJECTIVES: CPP crystals can be polymorphic (rhomboidal, parallelepiped: R/P), but some look like needles and could be taken as MSU under the bright field microscope. Birefringence of CPP crystals is weaker or absent compared with MSU crystals, but we aim to evaluate whether the grade of birefringence varies regarding the shape of the CPP crystal. METHODS: SF samples from patients with demonstrated acute CPP crystal arthritis were analysed by two observers, using a simple polarized light microscope equipped with two viewing stations. The analysis was performed simultaneously but in a blinded manner. Shape (needles or R/P) and the intensity of birefringence (absent, weak, moderate or MSU-like) were registered. χ2 trend test was used to evaluate the distribution of birefringence regarding the crystal shape. RESULTS: Two-hundred and fifty CPP crystals from 25 SF samples were analysed, well balanced between R/P and needles. The intensity of birefringence significantly differs between R/P or needles in the registries of both observers. R/P most often showed any grade of birefringence compared with needles, while no cases of MSU-like birefringence were found in acicular crystals. Both observers showed high agreement both in crystal shape and in intensity of birefringence. CONCLUSION: CPP crystals birefringence varies according to shape. Needle-shaped CPP crystals did not show strong birefringence, thus reinforcing the value of examining the samples with both ordinary and simple polarized light microscopes in differentiating them from MSU.

Low-dose computed tomography as diagnostic tool in calcium pyrophosphate deposition disease arthropathy: focus on ligamentous calcifications of the wrist.

OBJECTIVES: To identify specific morphologic features of calcium pyrophosphate deposition disease (pseudogout, CPPD) manifestations of the wrist as detected using low-dose CT-scans. METHODS: In this retrospective study 46 patients with arthritis of the wrist were included. All patients underwent a low dose CT scan of both wrists on a 320-row detector in volume scan mode. Individual radiation exposure was recorded for all patients. Two blinded raters independently evaluated osteoarthritis, cysts, erosions, calcifications (cartilage and ligaments separately) and carpal misalignment in 33 specified locations. An expert rheumatologist classified the patients as CPPD positive or negative. Fisher's exact test was applied to identify differences between both groups. Receiver operating characteristics (ROC) analyses with calculations of area under the curve (AUC) were carried out for both in the literature established and newly identified imaging findings for each rater individually. RESULTS: Twenty-seven patients were classified as CPPD, 19 patients as other diagnoses. Ligamentous calcifications were significantly more prevalent in the CPPD group (p<0.05). All non-ligamentous findings revealed no difference in frequency. AUC analysis for established findings (0.675; 0.619 - rater 1; 2) vs. ligamentous calcifications (0.786 both raters) showed a markedly higher diagnostic accuracy for the latter. Effective radiation exposure was determined to be 0.019-0.095 mSv per patient. CONCLUSIONS: Calcifications of carpal ligaments are highly specific morphologic features of CPPD arthropathy. Low-dose CT is a useful tool to detect these calcifications at a radiation exposure similar to a standard radiograph.

Issues in CPPD Nomenclature and Classification.

PURPOSE OF REVIEW: This paper covers confusion and challenges in the nomenclature of calcium pyrophosphate deposition disease. Clinicians, investigators, and patients are faced with a variety of terms that are used to describe CPPD and its phenotypes, and clarity is greatly needed to help advance research and patient care. Motivation for the upcoming development of CPPD classification criteria is reviewed. RECENT FINDINGS: EULAR proposed recommended terminology for CPPD in 2011. International Classification of Diseases (ICD-9 and ICD-10) billing codes identify definite or probable CPPD with variable accuracy depending on the clinical setting and comparator group. READ diagnostic codes have been employed to identify pseudogout in UK datasets but their accuracy has not been evaluated. CPPD classification criteria will provide a system for identifying a relatively homogenous group of patients to be included in clinical studies, enabling comparison of outcomes across studies. CPPD nomenclature remains challenging for clinicians, investigators, and patients. A lay-friendly definition of CPPD, using easily accessible terminology, would be welcome. CPPD classification criteria are a necessary step in moving forward CPPD clinical research and may involve a range of clinical, laboratory, and imaging modalities.

Inhibition of nucleotide pyrophosphatase/phosphodiesterase 1: implications for developing a calcium pyrophosphate deposition disease modifying drug.

Objectives: Calcium pyrophosphate deposition (CPPD) is associated with osteoarthritis and is the cause of a common inflammatory articular disease. Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (eNPP1) is the major ecto-pyrophosphatase in chondrocytes and cartilage-derived matrix vesicles (MVs). Thus, eNPP1 is a principle contributor to extracellular pyrophosphate levels and a potential target for interventions aimed at preventing CPPD. Recently, we synthesized and described a novel eNPP1-specific inhibitor, SK4A, and we set out to evaluate whether this inhibitor attenuates nucleotide pyrophosphatase activity in human OA cartilage. Methods: Cartilage tissue, chondrocytes and cartilage-derived MVs were obtained from donors with OA undergoing arthroplasty. The effect of SK4A on cell viability was assayed by the XTT method. eNPP1 expression was evaluated by western blot. Nucleotide pyrophosphatase activity was measured by a colorimetric assay and by HPLC analysis of adenosine triphosphate (ATP) levels. ATP-induced calcium deposition in cultured chondrocytes was visualized and quantified with Alizarin red S staining. Results: OA chondrocytes expressed eNPP1 in early passages, but this expression was subsequently lost upon further passaging. Similarly, significant nucleotide pyrophosphatase activity was only detected in early-passage chondrocytes. The eNPP1 inhibitor, SK4A, was not toxic to chondrocytes and stable in culture medium and human plasma. SK4A effectively inhibited nucleotide pyrophosphatase activity in whole cartilage tissue, in chondrocytes and in cartilage-derived MVs and reduced ATP-induced CPPD. Conclusion: Nucleotide analogues such as SK4A may be developed as potent and specific inhibitors of eNPP1 for the purpose of lowering extracellular pyrophosphate levels in human cartilage with the aim of preventing and treating CPPD disease.

Examination of concomitant glenohumeral pathologies in patients treated arthroscopically for calcific tendinitis of the shoulder and implications for routine diagnostic joint exploration.

BACKGROUND: Glenohumeral exploration is routinely performed during arthroscopic removal of rotator cuff calcifications in patients with calcific tendinitis of the shoulder (CTS). However, evidence on the prevalence of intraarticular co-pathologies is lacking and the benefit of glenohumeral exploration remains elusive. The aim of the present study was to assess and quantify intraoperative pathologies during arthroscopic removal of rotator cuff calcifications in order to determine whether standardized diagnostic glenohumeral exploration appears justified in CTS patients. METHODS: One hundred forty five patients undergoing arthroscopic removal of calcific depots (CD) that failed conservative treatment were included in a retrospective cohort study. Radiographic parameters including number/localization of calcifications and acromial types, intraoperative arthroscopic findings such as configuration of glenohumeral ligaments, articular cartilage injuries, and characteristics of calcifications and sonographic parameters (characteristics/localization of calcification) were recorded. RESULTS: One hundred forty five patients were analyzed. All CDs were removed by elimination with a blunt hook probe via "squeeze-and-stir-technique" assessed postoperatively via conventional X-rays. Neither subacromial decompression nor refixation of the rotator cuff were performed in any patient. Prevalence of glenohumeral co-pathologies, such as partial tears of the proximal biceps tendon (2.1%), superior labral tears from anterior to posterior (SLAP) lesions (1.4%), and/or partial rotator cuff tears (0.7%) was low. Most frequently, glenohumeral articular cartilage was either entirely intact (ICRS grade 0 (humeral head/glenoid): 46%/48%) or showed very mild degenerative changes (ICRS grade 1: 30%/26%). Two patients (1.3%) required intraarticular surgical treatment due to a SLAP lesion type III (n = 1) and an intraarticular rupture of CD (n = 1). CONCLUSIONS: Routine diagnostic glenohumeral exploration does not appear beneficial in arthroscopic treatment of CTS due to the low prevalence of intraarticular pathologies which most frequently do not require surgical treatment. Exploration of the glenohumeral joint in arthroscopic removal of CD should only be performed in case of founded suspicion of relevant concomitant intraarticular pathologies.

Comparison of outcomes after UKA in patients with and without chondrocalcinosis: a matched cohort study.

PURPOSE: Chondrocalcinosis can be associated with an inflammatory arthritis and aggressive joint destruction. There is uncertainty as to whether chondrocalcinosis represents a contraindication to unicompartmental knee arthroplasty (UKA). This study reports the outcome of a consecutive series of patients with chondrocalcinosis and medial compartment osteoarthritis treated with UKA matched to controls. METHODS: Between 1998 and 2008, 88 patients with radiological chondrocalcinosis (R-CCK) and 67 patients with histological chondrocalcinosis (H-CCK) were treated for end-stage medial compartment arthritis with Oxford UKA. One-to-two matching was performed to controls, treated with UKA, but without evidence of chondrocalcinosis. Functional outcome and implant survival were assessed in each group. RESULTS: The mean follow-up was 10 years. The mean Oxford Knee Score (OKS) at final follow-up was 43, 41 and 41 in H-CCK, R-CCK and control groups (change from baseline OKS was 21, 18 and 15, respectively). The change was significantly higher in H-CCK than in control but was not significantly different in R-CCK. Ten-year survival was 96 % in R-CCK, 86 % in H-CCK and 98 % in controls. Although the survival in H-CCK was significantly worse than in control, only one failure was due to disease progression. CONCLUSION: The presence of R-CCK does not influence functional outcome or survival following UKA. Pre-operative radiological evidence of CCK should not be considered to be a contraindication to UKA. H-CCK is associated with significantly improved clinical outcomes but also a higher revision rate compared with controls. LEVEL OF EVIDENCE: Case control study, Level III.

Unilateral anterior crossbite induces aberrant mineral deposition in degenerative temporomandibular cartilage in rats.

OBJECTIVE: To investigate whether mechanical stress induces mineral deposits that contribute to matrix degradation at the onset of osteoarthritis (OA) in temporomandibular joint (TMJ) cartilage. DESIGN: Female Spraguee-Dawley rats were subjected to an unilateral anterior crossbite (UAC) procedure. Histology, electron microscopy, and energy dispersive spectrometer (EDS) were used to examine cartilage matrix structures and composition of mineral deposit in the affected TMJ cartilage. Protein and/or RNA expression of phenotypic markers and mineralization modulators and matrix degradation was analyzed by immunohistochemistry and/or real-time PCR. Synthetic basic calcium phosphate (BCP) and calcium pyrophosphate dehydrate (CPPD) crystals were used to stimulate ATDC5 cells for their impact on cell differentiation and gene expression. RESULTS: Fragmented and disorganized collagen fibers, expanded fibrous spaces, and enhancement of matrix vesicle production and mineral deposition were observed in matrices surrounding hypertrophic chondrocytes in cartilage as early as 2-weeks post-UAC and exacerbated with time. The mineral deposits in TMJ cartilage at 12- and 20-weeks post-UAC had Ca/P ratios of 1.42 and 1.44, which are similar to the ratios for BCP. The expression of mineralization inhibitors, NPP1, ANK, CD73, and Matrix gla protein (MGP) was decreased from 2 to 8 weeks post-UAC, so were the chondrogenic markers, Col-2, Col-X and aggrecan. In contrast, the expression of tissue-nonspecific alkaline phosphatase (TNAP) and MMP13 was increased 4-weeks post-UAC. Treating ADTC5 cells with BCP crystals increased MMPs and ADAMTS5 expression, but reduced matrix production in a time-dependent manner. CONCLUSION: UAC induces deposition of BCP-like minerals in osteoarthritic cartilage, which can stimulate matrix degradation by promoting the expression of cartilage-degrading enzymes to facilitate OA progression.

Imaging of calcium pyrophosphate deposition disease.

Calcium pyrophosphate deposition disease (CPPD) is a common and clinically heterogeneous form of arthritis caused by the deposition of calcium pyrophosphate (CPP) crystals in articular tissues. The diagnosis of CPPD is supported by the presence of radiographic chondrocalcinosis; yet, conventional radiography detects only about 40 % of clinically important CPPD. Here, we critically review the recent literature on imaging in CPPD. New studies inform our use of conventional radiographic screening methodologies for CPPD and provide additional evidence for the utility of diagnostic ultrasound. Recent work also highlights the polyarticular nature of CPPD, its association with tissue damage, and the high prevalence of tendon involvement. While dual energy CT and diffraction-enhanced synchrotron imaging remain research tools, they present potential avenues for improved visualization of CPP deposits. Advances in imaging in CPPD will increase diagnostic accuracy and eventually result in better management of this common form of arthritis.

Pseudogout-associated inflammatory calcium pyrophosphate dihydrate microcrystals induce formation of neutrophil extracellular traps.

Pseudogout is an autoinflammatory condition triggered by calcium pyrophosphate dehydrate (CPPD) crystal deposition in the joints. The innate immune system is irritated by and responds to the presence of the crystals with an inflammatory response. The synovial fluid contains activated inflammatory macrophages and neutrophil granulocytes. Several details of crystal-induced macrophage activation were recently uncovered, but very little is known about interactions of CPPD crystals with neutrophils. In this study, we show that human neutrophils engulf CPPD crystals and form large amounts of neutrophil extracellular traps (NETs) in vitro. Released extracellular DNA binds myeloperoxidase and citrullinated histone H4. CPPD crystal-stimulated neutrophils and their nuclear DNA undergo morphological changes characteristic for NET formation. The ERK/MEK signaling pathway, heat shock protein 90, PI3K, and an intact cytoskeleton are required for CPPD-induced NET formation. Blocking crystal-activated respiratory burst has, however, no effect on NETs. Human neutrophils release IL-1ß and IL-8 in response to CPPD crystals, and blocking CXCR2, the main IL-8R, diminishes NET formation. Proinflammatory cytokines, TNF-α, GM-CSF, and IL-1ß, increase NET release by the crystals. Enhanced bacterial killing by CPPD-induced NETs demonstrates their ability to cause cellular damage. Our work documents and provides details about extracellular trap release in human neutrophils activated by CPPD microcrystals. We suggest that crystal-triggered NET formation can be a novel contributor to inflammatory conditions observed in CPPD crystal-driven synovitis.

The prevalence of and factors related to calcium pyrophosphate dihydrate crystal deposition in the knee joint.

OBJECTIVES: The purpose of this study was to reveal the accurate prevalence and related factors to the presence of calcium pyrophosphate dihydrate (CPPD) crystal deposition in cadaveric knee joints. DESIGN: Controlled laboratory study. METHODS: Six hundred and eight knees from 304 cadavers (332 male knees and 276 female knees, formalin fixed, Japanese anatomical specimens) were included in this study. The average age of the cadavers was 78.3 ± 10.7 years. Knees were macroscopically evaluated for the existence of CPPD, and the depth of cartilage degeneration of the femoro-tibial joint following the Outerbridge's classification. CPPD crystal was confirmed under Fourier transform infrared spectroscopy (FTIR) analysis using light microscopy. Statistical analysis was performed to reveal the correlation between the occurrence of CPPD deposition in the knee joint and gender, age, and the depth of cartilage degeneration of the femoro-tibial joint. RESULTS: The prevalence of grossly visible CPPD crystal was 13% (79 knees). In all of these knees, CPPD crystal was confirmed under FTIR analysis. Statistical analysis showed significant correlation between the occurrence of CPPD deposition and gender (P < 0.001), and depth of cartilage degeneration in the femoro-tibial joint (P < 0.001). In the cartilage degeneration positive knees (Over grade 3 in Outerbridge's classification), average age of CPPD deposition knee was significantly higher than CPPD negative knees. CONCLUSIONS: In this study, the prevalence of CPPD deposition disease was evaluated in a relatively large sample size of cadaveric knees. The prevalence of CPPD deposition disease was 13%, and was significantly correlated with the subject's age, gender, and severity of cartilage degeneration in the femoro-tibial joint.

Crystal induced arthropathies-a comparative study of 40 patients with apatite rheumatism, chondrocalcinosis and primary synovial chondromatosis.

Introduction: Apatite rheumatism (AR), chondrocalcinosis (Ch-C), and primary synovial chondromatosis (prSynCh) are regarded as distinct clinical entities. The introduction of the non-staining technique by Bély and Apáthy (2013) opened a new era in the microscopic diagnosis of crystal induced diseases, allowing the analysis of MSU (monosodium urate monohydrate) HA (calcium hydroxyapatite), CPPD (calcium pyrophosphate dihydrate) crystals, cholesterol, crystalline liquid lipid droplets, and other crystals in unstained sections of conventionally proceeded (aqueous formaldehyde fixed, paraffin-embedded) tissue samples. The aim of this study was to describe the characteristic histology of crystal deposits in AR, Ch-C, and prSynCh with traditional stains and histochemical reactions comparing with unstained tissue sections according to Bély and Apáthy (2013). Patients and methods: Tissue samples of 4 with apatite rheumatism (Milwaukee syndrome), 16 with chondrocalcinosis, and 20 with clinically diagnosed primary synovial chondromatosis were analyzed. Results and conclusion: Apatite rheumatism, chondrocalcinosis, and primary synovial chondromatosis are related metabolic disorders with HA and CPPD depositions. The authors assume that AR and Ch-C are different stages of the same metabolic disorder, which differ from prSynCh in amorphous mineral production, furthermore in the production of chondroid, osteoid and/or bone. prSynCh is a defective variant of HA and CPPD induced metabolic disorders with reduced mineralization capabilities, where the deficient mineralization is replaced by chondroid and/or bone formation. The non-staining technique of Bély and Apáthy proved to be a much more effective method for the demonstration of crystals in metabolic diseases than conventional stains and histochemical reactions.

Calcified Chondroid Mesenchymal Neoplasms.

Calcified chondroid mesenchymal neoplasms (CCMN) represent a morphologic spectrum of related tumors. Historically, chondroid matrix or chondroblastoma-like features have been described in soft tissue chondroma, tenosynovial giant cell tumors (especially of the temporomandibular joint (TMJ) region), and in a subset of tophaceous pseudogout. Recently, these tumors have been found to share FN1-receptor tyrosine kinase (RTK) fusions. This review discusses the clinical, morphologic, immunohistochemical, and molecular genetic features of CCMN. The distinction from morphologic mimics is also discussed.

Calcium pyrophosphate dihydrate deposition disease of the filum terminale.

INTRODUCTION: Calcium pyrophosphate dihydrate crystal deposition disease (CPPDD) is a rare benign inflammatory joint disorder characterized by the presence of calcium pyrophosphate dihydrate crystal in the interarticular and periarticular tissue. It has been rarely described with spinal localization. METHODS: A 50-year-old woman, affected by CPPDD, presented a progressive weakness of both lower limbs associated with neurogenic claudication. Neuroradiological examinations revealed the presence of two intradural calcified lesions at level L3-L4, with no post-contrast enhancement. RESULTS: Surgery was performed and the histopathological exams documented the presence of rod-shaped crystals embedded in a fibrocartilaginous stroma. The postoperative course was uneventful and the patient experienced complete symptoms relief with a 5-year follow-up. CONCLUSION: Intradural CPPD localization at the filum terminale is an extremely rare occurrence. Total removal should be preferably attempted with a long-term focal control of the disease as we observed in our case.

Calcium input potentiates the transforming growth factor (TGF)-beta1-dependent signaling to promote the export of inorganic pyrophosphate by articular chondrocyte.

Transforming growth factor (TGF)-ß1 stimulates extracellular PP(i) (ePP(i)) generation and promotes chondrocalcinosis, which also occurs secondary to hyperparathyroidism-induced hypercalcemia. We previously demonstrated that ANK was up-regulated by TGF-ß1 activation of ERK1/2 and Ca(2+)-dependent protein kinase C (PKCα). Thus, we investigated mechanisms by which calcium could affect ePP(i) metabolism, especially its main regulating proteins ANK and PC-1 (plasma cell membrane glycoprotein-1). We stimulated articular chondrocytes with TGF-ß1 under extracellular (eCa(2+)) or cytosolic Ca(2+) (cCa(2+)) modulations. We studied ANK, PC-1 expression (quantitative RT-PCR, Western blotting), ePP(i) levels (radiometric assay), and cCa(2+) input (fluorescent probe). Voltage-operated Ca(2+)-channels (VOC) and signaling pathways involved were investigated with selective inhibitors. Finally, Ank promoter activity was evaluated (gene reporter). TGF-ß1 elevated cCa(2+) and ePP(i) levels (by up-regulating Ank and PC-1 mRNA/proteins) in an eCa(2+) dose-dependent manner. TGF-ß1 effects were suppressed by cCa(2+) chelation or L- and T-VOC blockade while being mostly reproduced by ionomycin. In the same experimental conditions, the activation of Ras, the phosphorylation of ERK1/2 and PKCα, and the stimulation of Ank promoter activity were affected similarly. Activation of SP1 (specific protein 1) and ELK-1 (Ets-like protein-1) transcription factors supported the regulatory role of Ca(2+). SP1 or ELK-1 overexpression or blockade experiments demonstrated a major contribution of ELK-1, which acted synergistically with SP1 to activate Ank promoter in response to TGF-ß1. TGF-ß1 promotes input of eCa(2+) through opening of L- and T-VOCs, to potentiate ERK1/2 and PKCα signaling cascades, resulting in an enhanced activation of Ank promoter and ePP(i) production in chondrocyte.