Acute unilateral hip pain in fibrodysplasia ossificans progressiva (FOP)

Cell Senescence in Heterotopic Ossification

The formation of bone outside the normal skeleton, or heterotopic ossification (HO), occurs through genetic and acquired mechanisms. Fibrodysplasia ossificans progressiva (FOP), the most devastating genetic condition of HO, is due to mutations in the ACVR1/ALK2 gene and is relentlessly progressive. Acquired HO is mostly precipitated by injury or orthopedic surgical procedures but can also be associated with certain conditions related to aging. Cellular senescence is a hallmark of aging and thought to be a tumor-suppressive mechanism with characteristic features such as irreversible growth arrest, apoptosis resistance, and an inflammatory senescence-associated secretory phenotype (SASP). Here, we review possible roles for cellular senescence in HO and how targeting senescent cells may provide new therapeutic approaches to both FOP and acquired forms of HO.

Most Fractures Treated Nonoperatively in Individuals With Fibrodysplasia Ossificans Progressiva Heal With a Paucity of Flareups, Heterotopic Ossification, and Loss of Mobility

BACKGROUND

Fibrodysplasia ossificans progressiva (FOP) is an ultrarare genetic disorder with episodic and progressive heterotopic ossification. Tissue trauma is a major risk factor for flareups, heterotopic ossification (HO), and loss of mobility in patients with FOP. The International Clinical Council on FOP generally recommends avoiding surgery in patients with FOP unless the situation is life-threatening, because soft tissue injury can trigger an FOP flareup. Surprisingly little is known about flareups, HO formation, and loss of mobility after fractures of the normotopic (occurring in the normal place, distinct from heterotopic) skeleton when treated nonoperatively in patients with FOP.

QUESTIONS/PURPOSES

(1) What proportion of fractures had radiographic evidence of union (defined as radiographic evidence of healing at 6 weeks) or nonunion (defined as the radiographic absence of a bridging callus at 3 years after the fracture)? (2) What proportion of patients had clinical symptoms of an FOP flareup because of the fracture (defined by increased pain or swelling at the fracture site within several days after closed immobilization)? (3) What proportion of patients with fractures had radiographic evidence of HO? (4) What proportion of patients lost movement after a fracture?

METHODS

We retrospectively identified 36 patients with FOP from five continents who sustained 48 fractures of the normotopic skeleton from January 2001 to February 2021, who were treated nonoperatively, and who were followed for a minimum of 18 months after the fracture and for as long as 20 years, depending on when they sustained their fracture during the study period. Five patients (seven fractures) were excluded from the analysis to minimize cotreatment bias because these patients were enrolled in palovarotene clinical trials (NCT02190747 and NCT03312634) at the time of their fractures. Thus, we analyzed 31 patients (13 male, 18 female, median age 22 years, range 5 to 57 years) who sustained 41 fractures of the normotopic skeleton that were treated nonoperatively. Patients were analyzed at a median follow-up of 6 years (range 18 months to 20 years), and none was lost to follow-up. Clinical records for each patient were reviewed by the referring physician-author and the following data for each fracture were recorded: biological sex, ACVR1 gene pathogenic variant, age at the time of fracture, fracture mechanism, fracture location, initial treatment modality, prednisone use at the time of the fracture as indicated in the FOP Treatment Guidelines for flare prevention (2 mg/kg once daily for 4 days), patient-reported flareups (episodic inflammatory lesions of muscle and deep soft connective tissue characterized variably by swelling, escalating pain, stiffness, and immobility) after the fracture, follow-up radiographs of the fracture if available, HO formation (yes or no) as a result of the fracture determined at a minimum of 6 weeks after the fracture, and patient-reported loss of motion at least 6 months after and as long as 20 years after the fracture. Postfracture radiographs were available in 76% (31 of 41) of fractures in 25 patients and were independently reviewed by the referring physician-author and senior author for radiographic criteria of fracture healing and HO.

RESULTS

Radiographic healing was noted in 97% (30 of 31) of fractures at 6 weeks after the incident fracture. Painless nonunion was noted in one patient who sustained a displaced patellar fracture and HO. In seven percent (three of 41) of fractures, patients reported increased pain or swelling at or near the fracture site within several days after fracture immobilization that likely indicated a site-specific FOP flareup. The same three patients reported a residual loss of motion 1 year after the fracture compared with their prefracture status. HO developed in 10% (three of 31) of the fractures for which follow-up radiographs were available. Patient-reported loss of motion occurred in 10% (four of 41) of fractures. Two of the four patients reported noticeable loss of motion and the other two patients reported that the joint was completely immobile (ankylosis).

CONCLUSION

Most fractures treated nonoperatively in individuals with FOP healed with few flareups, little or no HO, and preservation of mobility, suggesting an uncoupling of fracture repair and HO, which are two inflammation-induced processes of endochondral ossification. These findings underscore the importance of considering nonoperative treatment for fractures in individuals with FOP. Physicians who treat fractures in patients with FOP should consult with a member of the International Clinical Council listed in the FOP Treatment Guidelines ( https://www.iccfop.org ).

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Painful and restricted hip due to myositis ossificans circumscripta of the pectineus muscle after pelvic fracture: A case report

RATIONALE

Myositis ossificans circumscripta (MOC) is a rare disorder that causes heterotopic bone formation in soft tissues. It usually occurs after trauma and affects large muscles of the extremities. MOC of the pectineus muscle is extremely rare and has not been reported to be treated surgically.

PATIENT CONCERNS

A 52-year-old woman presented with left hip pain and dysfunction 4 months after a traffic accident that caused pelvic and humeral fractures and cerebral hemorrhage.

DIAGNOSES

Radiological imaging revealed isolated ossification of the left pectineus muscle. The patient was diagnosed with MOC.

INTERVENTIONS

The patient underwent surgical resection of the ossified pectineus muscle followed by local radiation and medical therapy.

OUTCOMES

At 12 months postoperatively, she was asymptomatic and had normal hip function. No recurrence was observed on radiography.

LESSONS

MOC of the pectineus muscle is a rare condition that can cause severe hip dysfunction. Surgical resection combined with radiation and anti-inflammatory drugs can be an effective treatment option for patients who do not respond to conservative management.

Diminished muscle integrity in patients with fibrodysplasia ossificans progressiva assessed with at-home electrical impedance myography

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder involving skeletal dysplasia and heterotopic ossification (HO) of muscle and connective tissue. We aimed to define a novel biomarker in FOP that enables reliable assessment of musculoskeletal tissue integrity. Considering logistical difficulties that FOP patients often face, our goal was to identify an at-home biomarker technique. Electrical impedance myography (EIM) is a non-invasive, portable method that can inform on muscle health. 15 FOP patients (age 10-52) and 13 healthy controls were assessed. Using EIM, multiple muscle groups were characterized per participant in a 45-min period. The Cumulative Analogue Joint Involvement Scale (CAJIS) was implemented to determine mobility burden severity. We additionally evaluated physical activity levels via a Patient-Reported Outcomes Measurement Information System (PROMIS)-based questionnaire. Relative to controls, FOP patients demonstrated significantly lower regional and whole-body phase values at 50 kHz and 100 kHz, indicating more diseased muscle tissue. Lower whole-body phase and reactance values, and higher resistance values, were associated with greater FOP burden (CAJIS score range: 4-30) and lower physical activity levels at 50 kHz and 100 kHz. This study points to the potential utility of EIM as a clinical biomarker tool capable of characterizing muscle integrity in FOP.

Mechanisms of bone pain: Progress in research from bench to bedside

The field of research on pain originating from various bone diseases is expanding rapidly, with new mechanisms and targets asserting both peripheral and central sites of action. The scope of research is broadening from bone biology to neuroscience, neuroendocrinology, and immunology. In particular, the roles of primary sensory neurons and non-neuronal cells in the peripheral tissues as important targets for bone pain treatment are under extensive investigation in both pre-clinical and clinical settings. An understanding of the peripheral mechanisms underlying pain conditions associated with various bone diseases will aid in the appropriate application and development of optimal strategies for not only managing bone pain symptoms but also improving bone repairing and remodeling, which potentially cures the underlying etiology for long-term functional recovery. In this review, we focus on advances in important preclinical studies of significant bone pain conditions in the past 5 years that indicated new peripheral neuronal and non-neuronal mechanisms, novel targets for potential clinical interventions, and future directions of research.

BMP signaling and skeletal development in fibrodysplasia ossificans progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic disease caused by increased BMP pathway signaling due to mutation of ACVR1, a bone morphogenetic protein (BMP) type 1 receptor. The primary clinical manifestation of FOP is extra-skeletal bone formation (heterotopic ossification) within soft connective tissues. However, the underlying ACVR1 mutation additionally alters skeletal bone development and nearly all people born with FOP have bilateral malformation of the great toes as well as other skeletal malformations at diverse anatomic sites. The specific mechanisms through which ACVR1 mutations and altered BMP pathway signaling in FOP influence skeletal bone formation during development remain to be elucidated; however, recent investigations are providing a clearer understanding of the molecular and developmental processes associated with ACVR1-regulated skeletal formation.

Pain Phenotypes in Rare Musculoskeletal and Neuromuscular Diseases

For patients diagnosed with a rare musculoskeletal or neuromuscular disease, pain may transition from acute to chronic; the latter yielding additional challenges for both patients and care providers. We assessed the present understanding of pain across a set of ten rare, noninfectious, noncancerous disorders; Osteogenesis Imperfecta, Ehlers-Danlos Syndrome, Achondroplasia, Fibrodysplasia Ossificans Progressiva, Fibrous Dysplasia/McCune-Albright Syndrome, Complex Regional Pain Syndrome, Duchenne Muscular Dystrophy, Infantile- and Late-Onset Pompe disease, Charcot-Marie-Tooth Disease, and Amyotrophic Lateral Sclerosis. Through the integration of natural history, cross-sectional, retrospective, clinical trials, & case studies we described pathologic and genetic factors, pain sources, phenotypes, and lastly, existing therapeutic approaches. We highlight that while rare diseases possess distinct core pathologic features, there are a number of shared pain phenotypes and mechanisms that may be prospectively examined and therapeutically targeted in a parallel manner. Finally, we describe clinical and research approaches that may facilitate more accurate diagnosis, monitoring, and treatment of pain as well as elucidation of the evolving nature of pain phenotypes in rare musculoskeletal or neuromuscular illnesses.

Suppressed prefrontal cortex oscillations associate with clinical pain in fibrodysplasia ossificans progressiva

Background

Pain is a highly prevalent symptom experienced by patients across numerous rare musculoskeletal conditions. Much remains unknown regarding the central, neurobiological processes associated with clinical pain in musculoskeletal disease states. Fibrodysplasia ossificans progressiva (FOP) is an inherited condition characterized by substantial physical disability and pain. FOP arises from mutations of the bone morphogenetic protein (BMP) receptor Activin A receptor type 1 (ACVR1) causing patients to undergo painful flare-ups as well as heterotopic ossification (HO) of skeletal muscles, tendons, ligaments, and fascia. To date, the neurobiological processes that underlie pain in FOP have rarely been investigated. We examined pain and central pain mechanism in FOP as a model primary musculoskeletal condition. Central nervous system (CNS) functional properties were investigated in FOP patients (N = 17) stratified into low (0–3; 0–10 Scale) and high (≥ 4) pain cohorts using functional near-infrared spectroscopy (fNIRS). Associations among clinical pain, mental health, and physical health were also quantified using responses derived from a battery of clinical questionnaires.

Results

Resting-state fNIRS revealed suppressed power of hemodynamic activity within the slow-5 frequency sub-band (0.01–0.027 Hz) in the prefrontal cortex in high pain FOP patients, where reduced power of slow-5, prefrontal cortex oscillations exhibited robust negative correlations with pain levels. Higher clinical pain intensities were also associated with higher magnitudes of depressive symptoms.

Conclusions

Our findings not only demonstrate a robust coupling among prefrontal cortex functionality and clinical pain in FOP but lays the groundwork for utilizing fNIRS to objectively monitor and central pain mechanisms in FOP and other musculoskeletal disorders.

Skeletal malformations and developmental arthropathy in individuals who have fibrodysplasia ossificans progressiva

RATIONALE

Fibrodysplasia ossificans progressiva (FOP) is primarily a disease of progressive heterotopic ossification (HO) leading to impaired mobility throughout life. An additional diagnostic feature is a characteristic malformation of the great toes. The culpable gene for FOP,ACVR1 (activin A receptor type 1) has a clear effect on the induction of extra-skeletal bone formation. However, this bone morphogenetic protein (BMP) pathway receptor is expressed widely throughout skeletal development and has a seminal role in axial and appendicular chondrogenesis, prompting suspicion of widespread bone and joint defects in those with ACVR1 mutations.

MATERIALS AND METHODS

We analyzed baseline whole body (minus skull) computed tomographic (CT) scans of 113 individuals with classic clinical features of FOP and the ACVR1 (R206H) mutation who were enrolled in a non-interventional natural history study ((NCT02322255)) for skeletal malformations, atypical morphology, intra-articular synovial osteochondromatosis, developmental arthropathy, and associated degenerative joint phenotypes. Individuals were evaluated in three age groups: 4-13; 14-25; and 25-56 years old, based on historical models of FOP disease progression.

RESULTS

We found widespread evidence of developmental arthropathy throughout the axial and appendicular skeleton in all age groups (61M, 52F; ages: 4-56 years). Asymmetric narrowing and subchondral sclerosis were present throughout the joints of the normotopic skeleton and osteophytes were common in the hips and knees of individuals who have FOP in all age groups. The costovertebral joints, intervertebral facet joints, and proximal tibio-fibular joints frequently showed partial or total intra-articular ankylosis, particularly after age 13. The hips of FOP subjects are frequently malformed and dysplastic. We also found evidence of degenerative joint phenotypes after age 13, particularly in the spine, sacro-iliac joints, and lower limbs.

CONCLUSIONS

The effects of ACVR1 mutation on the normotopic skeletons of individuals who have FOP extend beyond malformation of the great toes and include both morphological defects and developmental arthropathy. Associated degenerative joint disease occurring at multiple sites starts in adolescence and progresses throughout life. These phenotypes appear to be uncoupled from heterotopic bone formation, indicating a potential role for ACVR1 in the development and progression of degenerative joint disease.

SIGNIFICANCE

FOP is a disease of not only progressive heterotopic ossification, but also widespread and extensive developmental arthropathy and associated degenerative joint disease. These findings have relevance for understanding the natural history of FOP and for designing and evaluating clinical trials with emerging therapeutics.

Natural history of fibrodysplasia ossificans progressiva: cross-sectional analysis of annotated baseline phenotypes

BACKGROUND

Fibrodysplasia Ossificans Progressiva (FOP; OMIM#135100) is an ultra-rare, severely disabling genetic disease characterized by congenital malformation of the great toes and progressive heterotopic ossification (HO) in muscles, tendons, ligaments, fascia, and aponeuroses often preceded by painful, recurrent soft tissue swelling (flare-ups). The formation of HO leads to progressive disability, severe functional limitations in joint mobility, and to a shortened life-span. In this prospective natural history study, we describe the baseline, cross-sectional disease phenotype of 114 individuals with FOP.

METHODS

All subjects underwent protocol-specified baseline assessments to determine their disease status. Cross-sectional analyses were performed using linear regression in which functional evaluations (Cumulative Analogue Joint Involvement Scale [CAJIS] and the FOP-Physical Function Questionnaire [FOP-PFQ]) and the burden of HO as measured by low-dose whole body CT (volume of HO and number of body regions with HO) were assessed.

RESULTS

Findings from 114 subjects (age range 4 to 56 years) were evaluated. While subject age was significantly (p < 0.0001) correlated with increased CAJIS (r = 0.66) and FOP-PFQ scores (r = 0.41), the estimated mean increases per year (based on cross-sectional average changes over time) were small (0.47 units and 1.2%, respectively). There was also a significant (p < 0.0001) correlation between baseline age and HO volume (r = 0.56), with an estimated mean increase of 25,574 mm³/year. There were significant (p < 0.0001) correlations between the objective assessment of HO volume and clinical assessments of CAJIS (r = 0.57) and FOP-PFQ (r = 0.52).

CONCLUSIONS

Based on the cross-sectional analysis of the baseline data, functional and physical disability as assessed by CAJIS and the FOP-PFQ increased over time. Although longitudinal data are not yet available, the cross-sectional analyses suggest that CAJIS and FOP-PFQ are not sensitive to detect substantial progression over a 1- to 2-year period. Future evaluation of longitudinal data will test this hypothesis. The statistically significant correlations between HO volume and the functional endpoints, and the estimated average annual increase in total HO volume, suggest that the formation of new HO will be measurable over the relative short-term course of a clinical trial, and represents an endpoint that is clinically meaningful to patients.

TRIAL REGISTRATION

This study ( NCT02322255 ) was first posted on 23 December, 2014.

Longitudinal Evaluation of Pain, Flare-Up, and Emotional Health in Fibrodysplasia Ossificans Progressiva: Analyses of the International FOP Registry

Fibrodysplasia ossificans progressiva (FOP) is an ultra‐rare, inherited, connective tissue disease with ∼800 documented cases worldwide. The principal pathological feature of FOP is the transition of skeletal muscle, tendons, ligaments, and fascia into cartilage and bone. This heterotopic ossification (HO) is often preceded by painful soft tissue swellings or flare‐ups that may last several months. For many individuals, experiencing a flare‐up may represent a worsening of their condition and contribute to feelings of anxiety or suppressed affect, both of which are well‐recognized to exacerbate pain perception. To date, much remains unknown regarding the dynamics of pain and emotional health in FOP during flare‐up and also quiescent, non–flare‐up disease phases. In order to elucidate the occurrence and effect of pain in FOP, this study analyzed Patient‐Reported Outcomes Measurement Information System–based questionnaires completed by 99 patients participating in the international FOP Registry over a 30‐month period. We observed that although moderate to severe pain (≥4, 0 to 10 pain scale) was commonly associated with flare‐ups (56% to 67%), surprisingly, 30% to 55% of patients experienced similar pain levels during non–flare‐up states. In those patients reporting pain levels of ≥4, 45% to 74% of patients report experiencing anxiety, depression, or irritability, with 36% to 48% reporting emotional problems during no to mild pain states. Furthermore, independent of the flare‐up status, the severity of pain in FOP patients was found to be significantly anti‐correlated with emotional health, physical health, and overall quality‐of‐life. These findings strongly suggest the need for an improved understanding of pain and emotional health in FOP during flare‐up and quiescent periods. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.