Experimental influenza B viral myositis

Benign Acute Childhood Myositis in a Pediatric Patient Post Influenza B Infection

Benign acute childhood myositis (BACM) is a mild and self-limited sudden onset of lower extremity pain during or following recovery from a viral illness. It is characterized by difficulty walking due to severe bilateral calf pain, which usually resolves in three days. It is typically appreciated during times of large influenza outbreaks and epidemics. The most severe complication can be rhabdomyolysis without proper treatment and can lead to renal damage and potential renal failure. There are limited reported cases of BACM and therefore no clear guidelines in the treatment or management of the condition. This case is unique in the sense that the patient had leg pain the entire month prior to presentation in the absence of trauma or injury, and it is believed that the pre-existing myalgia may have been exacerbated by an upper respiratory infection (URI) that started a few weeks after the leg pain onset. In addition, this patient's creatine kinase peaked at over 13,000 U/L, which is three to five times higher than the average of other reported children with this condition. The patient is a five-year-old male who presented to the emergency department with bilateral leg pain and difficulty ambulating. His guardian reported that the leg pain began one month prior to presentation and worsened to the point where he could no longer ambulate, following a fever and cough that began one week prior to presentation. A respiratory viral panel was positive for influenza B, and initial creatine kinase (CK) levels were greater than 10,000. A diagnosis of BACM was made, and supportive care was initiated. BACM is an infrequent complication following a viral infection that is typically treatable with hydration management and routine CK monitoring. Symptoms of BACM are usually limited to muscle pain and weakness, but it can progress to rhabdomyolysis and renal failure if not managed properly. It is therefore crucial that physicians monitor CK values daily until a downtrend is noticed and symptoms begin to resolve.

Neuromuscular Complications of SARS-CoV-2 and Other Viral Infections

In this article we review complications to the peripheral nervous system that occur as a consequence of viral infections, with a special focus on complications of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We discuss neuromuscular complications in three broad categories; the direct consequences of viral infection, autoimmune neuromuscular disorders provoked by viral infections, and chronic neurodegenerative conditions which have been associated with viral infections. We also include discussion of neuromuscular disorders that are treated by immunomodulatory therapies, and how this affects patient susceptibility in the current context of the coronavirus disease 2019 (COVID-19) pandemic. COVID-19 is associated with direct consequences to the peripheral nervous system via presumed direct viral injury (dysgeusia/anosmia, myalgias/rhabdomyolysis, and potentially mononeuritis multiplex) and autoimmunity (Guillain Barré syndrome and variants). It has important implications for people receiving immunomodulatory therapies who may be at greater risk of severe outcomes from COVID-19. Thus far, chronic post-COVID syndromes (a.k.a: long COVID) also include possible involvement of the neuromuscular system. Whether we may observe neuromuscular degenerative conditions in the longer term will be an important question to monitor in future studies.

Benign acute childhood myositis associated with influenza A/B in the paediatric emergency department and the efficacy of early-onset oseltamivir

AIM

To investigate the association of benign acute childhood myositis (BACM) with respiratory viruses. Also, we aimed to assess the effect of antiviral treatment on the improvement and complications.

METHODS

This study was conducted at an urban-academic emergency department during four influenza-seasons (2016-2019), retrospectively. Demographics, clinical findings, laboratories, metabolic disease analyses and serological features were extracted from the medical records. Treatments, complications and outcomes were also recorded.

RESULTS

A total of 114 children were included. The median age was 7.0 (min 1.25-max 17) years and 78.9% were male. The most common symptoms were leg pain (91.2%), anorexia (54.4%), fever (45.6%), sore throat (42.1%) and walking difficulty (32.5%). On admission, the median creatine phosphokinase level was 3332 IU/L (range, 1634-50 185), median aspartate aminotransferase 107 U/L (range, 38-1798). In the multiplex polymerase chain reaction analysis, 40.4% influenza B, 36.8% influenza A, 7.8% adenovirus, 7.8% parainfluenza virus, 5.3% rhinovirus, 5.3% respiratory syncytial virus and 1.8% Mycoplasma pneumoniae were detected. Rhabdomyolysis was developed in 6.7% and acute renal failure was seen in two patients. Oseltamivir was given in 44 (38.6%) patients who had influenza A/B. Metabolic disease screening tests were performed in 33.3% of patients and metabolic diseases were detected in 4 (3.5%) patients. The median recovery time was lower in patients with oseltamivir treatment (4 (min 2-max 5) - 5 (min 3-max 10) days) (P < 0.001).

CONCLUSION

Rhabdomyolysis is more common in BACM due to the influenza A virus. The early use of oseltamivir treatment was significantly associated with a shorter recovery time.

Influenza A-induced rhabdomyolysis with acute renal failure following a deep tissue massage

We describe a unique case of severe influenza A-induced rhabdomyolysis in a previously healthy 39-year-old man, who developed symptoms immediately following a 2-hour deep-tissue massage and improved with oseltamivir and intravenous fluids. This case describes a possible temporal association between tissue damage secondary to deep tissue massage and the subsequent exacerbation of rhabdomyolysis in the setting of an influenza A infection. Biological evidence of muscle cell viral invasion with massage supports the possibility of elevated influenza A pathogenicity.

Influenza-associated myositis: a single-centre, 5-year retrospective study

We aimed to describe the clinical epidemiology of influenza-associated myositis (IAM) over a 5-year period. We identified ICD-10-coded myositis cases retrospectively 2011-2015 and performed limited chart reviews. We excluded myositis with non-viral causes and cross-referenced with laboratory records of influenza tests to identify confirmed IAM. We defined probable IAM as viral myositis occurring during the influenza season without alternative cause. We described epidemiological and clinical features of IAM and compared IAM with all hospitalised influenza. We identified 283 cases of viral myositis with seasonal peaks (May to October, 85% of cases); 69 were tested for influenza, 52 (78%) were positive. Given the strong seasonality concurrent with the influenza season, we estimated that 80% (95% CI 76-85) of viral myositis is attributable to IAM annually. Of 226 cases of IAM, 21% (n = 49) were confirmed and the remaining probable. IAM was associated with being male (82%), aged 5-9 (73%), and influenza B (86%). The majority had bilateral calf pain; mean creatinine kinase (CK) value was 3579 U/L, and no cases had renal impairment.Conclusion: Childhood viral myositis shows strong association with the influenza season. IAM is clinically stereotyped, age restricted, and benign in most and strongly associated with influenza B. What is Known: • Childhood viral myositis has been reported in association with influenza for decades, more frequently with influenza B and in school-aged children. What is New: • Here, we show over a 5-year period that viral myositis is strongly seasonal with up to 80% of cases attributable to influenza. • Influenza-associated myositis (IAM) typically occurs in boys, aged 5-9 years, with influenza B and is most often benign. Early clinical recognition may avoid unnecessary treatment and testing.

Differential diagnosis of idiopathic inflammatory myopathies in adults - the first step when approaching a patient with muscle weakness

Despite its misleading adjective, the most commonly used diagnostic criteria of idiopathic inflammatory myopathies (IIM) are applicable only after all other non-autoimmune muscle diseases have been excluded. It makes differential diagnosis the first step when approaching a patient with muscle weakness. This article is designed to list the most common conditions from which to differentiate in rheumatological care. In fact, many patients with the diseases described here have been initially misdiagnosed with IIM. For the purpose of this article, only the most commonly found and important conditions according to the authors are listed with the essence of information; other autoimmune muscle diseases, such as sarcoidosis and eosinophilic myositis, are not portrayed. The attached bibliography may serve as a source, when further exploration of a specific subject is needed.

Benign Acute Childhood Myositis: Perplexing Complication after Acute Viral Pharyngitis

Benign acute childhood myositis (BACM) is a rare transient condition that occurs in children during the early convalescent phase of a viral upper respiratory infection. BACM is self-limiting and characterized by sudden-onset bilateral calf pain that leads to difficulty in walking. We report a case of a 5-year-old boy with BACM who presented with acute-onset bilateral calf pain after a resolved episode of viral pharyngitis and subsequently refused to walk. With conservative treatment, the patient recovered completely after approximately 1 week. Although perplexing and challenging for clinicians unfamiliar with BACM, awareness of this rare clinical condition is essential to preventing unnecessary investigations and reassuring the patient and parents of its excellent prognosis.

Analysis of Clinical Manifestations and Laboratory Findings in Children with Influenza B-Associated Myositis: A Single Center Study

Background

Influenza-associated myositis (IAM) is a rare and poorly recognized complication of influenza infection in children, and is characterized by acute onset of severe pain in the lower extremities and a refusal to ambulate walk. We sought to understand the association between IAM and influenza B infection and to investigate its clinical and laboratory characteristics in affected children.

Methods

Influenza B-associated myositis (IBAM) cases diagnosed in the pediatrics department of Wonkwang University Hospital from January 2010 and March 2016 were analyzed retrospectively.

Results

Medical records of affected children were examined, and clinical characteristics and laboratory findings were recorded. Of the 536 children diagnosed with influenza B infection, 47 children complained of bilateral calf pain with or without gait disturbance. All children exhibited elevated serum aspartate aminotransferase (AST) level. The median serum creatine kinase (CK) and lactate dehydrogenase (LDH) levels, reportedly elevated in myositis, were 2,597 IU/L and 678 IU/L, respectively. While the immunofluorescence test results were negative for some patients, the polymerase chain reaction test results indicated influenza B infection in all 47 children. At the time of hospital discharge, the patients' symptoms had resolved, and their CK levels had improved.

Conclusion

IBAM was generally benign and short, and although the blood AST, CK, and LDH levels were markedly high, the erythrocyte sedimentation rate and C-reactive protein levels were normal. Further, the duration of IBAM symptoms correlated with the duration of fever. The IBAM-associated clinical and laboratory findings are highly characteristic and may allow its rapid diagnosis during the influenza season.

Aging augments the impact of influenza respiratory tract infection on mobility impairments, muscle-localized inflammation, and muscle atrophy

Although the influenza virus only infects the respiratory system, myalgias are commonly experienced during infection. In addition to a greater risk of hospitalization and death, older adults are more likely to develop disability following influenza infection; however, this relationship is understudied. We hypothesized that upon challenge with influenza, aging would be associated with functional impairments, as well as upregulation of skeletal muscle inflammatory and atrophy genes. Infected young and aged mice demonstrated decreased mobility and altered gait kinetics. These declines were more prominent in hind limbs and in aged mice. Skeletal muscle expression of genes involved in inflammation, as well as muscle atrophy and proteolysis, increased during influenza infection with an elevated and prolonged peak in aged mice. Infection also decreased expression of positive regulators of muscle mass and myogenesis components to a greater degree in aged mice. Gene expression correlated to influenza-induced body mass loss, although evidence did not support direct muscle infection. Overall, influenza leads to mobility impairments with induction of inflammatory and muscle degradation genes and downregulation of positive regulators of muscle. These effects are augmented and prolonged with aging, providing a molecular link between influenza infection, decreased resilience and increased risk of disability in the elderly.

Clinical Implications and Hospital Outcome of Immune-Mediated Myositis in Horses

BACKGROUND

Immune-mediated myositis (IMM) is a cause of rhabdomyolysis, stiffness, and muscle atrophy predominantly affecting Quarter horses. Limited information is available with regard to outcome, prognostic indicators, and associations with concurrent diseases.

HYPOTHESIS/OBJECTIVES

To report outcomes and associations between outcome and clinical and laboratory parameters, and presence of concurrent illness.

ANIMALS

Sixty-eight horses; 52 Quarter horses and related breeds and 16 other breeds.

METHODS

Retrospective cohort study (1991-2014). Medical records of horses with histological diagnosis of IMM were reviewed. Data recovery included signalment, laboratory variables, therapy, and outcome. Logistic regression was used to quantify the association between potential prognostic factors and survival to discharge.

RESULTS

Quarter horses were younger (mean < 4 years, range 3 months-21 years) than other breeds (mean < 10 years, range 1-23 years). Pathogens causing concurrent or recent infection included S. equi equi, S. equi zooepidemicus, C. pseudotuberculosis, Anaplasma phagocytophilum, herpes virus-1, and influenza. The most common clinical signs consisted of rapidly progressive diffuse symmetrical muscle atrophy (80%), stiff gait (74%), and fever (44%). All horses that received medical therapy immediately upon admission survived to discharge (survival proportion = 87%). Leucocytosis was a common finding (60%). Horses with concurrent fever and other illness had a poor prognosis for hospital discharge.

CONCLUSIONS AND CLINICAL IMPORTANCE

Horses with IMM can have a favorable outcome. Horses with concurrent fever and another illness had decreased probability of survival to discharge.

Acute hepatitis and myositis associated with Erythema infectiosum by Parvovirus B19 in an adolescent

Background

Erythema infectiosum is the most common clinical manifestation of Parvovirus B19 infection although it has also been associated with rheumatologic diseases and various types of systemic vasculitides. Acute hepatitis and benign myositis however are rarely reported in association with Parvovirus B19 infection.

Case presentation

Here we report a 14-year old male, who developed acute hepatitis and benign myositis associated with erythema infectiosum following Parvovirus B19 infection.

Conclusion

Parvovirus B19 infection has rarely been associated with acute hepatitis and exceptionally rarely with benign myositis. Parvovirus B19 should be considered in the differential diagnosis of acute non-A to E hepatitis and in the case of acute benign myositis presenting with a rash especially in children.

Neurologic aspects of influenza viruses

Although influenza A and B viruses are primarily known as respiratory viruses and mainly infected only the upper respiratory tract in humans, patients with influenza often develop signs and symptoms that are not due to the respiratory system. Frequently individuals with influenza develop headaches, meningismus, and even seizures in addition to their typical respiratory symptoms. In the past decades, influenza viruses have also been associated with serious non-respiratory signs. The famous 1918 strain of influenza was associated with von Economo's encephalitis lethargica and postencephalitic parkinsonism. In the 1960s influenza virus infections in children were associated with Reye's syndrome characterized often by fatty non-inflammatory hepatic disease and an encephalopathy with marked non-inflammatory cerebral edema. Intermittently children with influenza develop focal myalgia and myositis. Guillain–Barré syndrome was epidemiologically associated with the 1978 killed influenza vaccine but not subsequent vaccines. Although occasional children with influenza have developed encephalopathy, from 2000 through 2004 there was an increase in the number of serious cases of acute necrotizing encephalopathy accompanying infection with the influenza A 2009 strain. The current H5N1 strain of bird influenza occasionally infects humans with a high mortality rate and some appear to have central nervous signs. This chapter explores what is known about these influenza neurologic associations.

Productive infection of human skeletal muscle cells by pandemic and seasonal influenza A(H1N1) viruses

Besides the classical respiratory and systemic symptoms, unusual complications of influenza A infection in humans involve the skeletal muscles. Numerous cases of acute myopathy and/or rhabdomyolysis have been reported, particularly following the outbreak of pandemic influenza A(H1N1) in 2009. The pathogenesis of these influenza-associated myopathies (IAM) remains unkown, although the direct infection of muscle cells is suspected. Here, we studied the susceptibility of cultured human primary muscle cells to a 2009 pandemic and a 2008 seasonal influenza A(H1N1) isolate. Using cells from different donors, we found that differentiated muscle cells (i. e. myotubes) were highly susceptible to infection by both influenza A(H1N1) isolates, whereas undifferentiated cells (i. e. myoblasts) were partially resistant. The receptors for influenza viruses, α2-6 and α2-3 linked sialic acids, were detected on the surface of myotubes and myoblasts. Time line of viral nucleoprotein (NP) expression and nuclear export showed that the first steps of the viral replication cycle could take place in muscle cells. Infected myotubes and myoblasts exhibited budding virions and nuclear inclusions as observed by transmission electron microscopy and correlative light and electron microscopy. Myotubes, but not myoblasts, yielded infectious virus progeny that could further infect naive muscle cells after proteolytic treatment. Infection led to a cytopathic effect with the lysis of muscle cells, as characterized by the release of lactate dehydrogenase. The secretion of proinflammatory cytokines by muscle cells was not affected following infection. Our results are compatible with the hypothesis of a direct muscle infection causing rhabdomyolysis in IAM patients.

Three cases of acute myositis in adults following influenza-like illness during the H1N1 pandemic

Acute viral myositis is a rare condition that occurs during the recovery phase of an illness, most commonly influenza. It is characterized by muscle pain and weakness with an isolated laboratory finding of elevated serum creatine kinase (CK). We describe three previously healthy patients who were hospitalized after developing myositis following influenza-like illness during the 2009 influenza A (H1N1) virus pandemic. All experienced myalgias and weakness in all four extremities, including distal upper extremities, associated with an elevated CK level that resolved along with their myalgias and weakness within one week with supportive care. These cases serve as a reminder that influenza-related myositis may have atypical characteristics depending on the strain of influenza, and clinicians should be open to this possibility when new outbreaks occur.

A large outbreak of influenza B-associated benign acute childhood myositis in Germany, 2007/2008

BACKGROUND

Benign acute childhood myositis (BACM) is a rare syndrome associated with various viral infections. Bilateral calve pain may lead to inability to walk. During winter 2007/2008, we investigated a nationwide outbreak of influenza-associated BACM (IA-BACM) to identify etiologic (sub)type, describe the course of disease, and explore how well the syndrome is known among physicians.

METHODS

We performed retrospective and prospective case finding in all German federal states. Physicians returned patient-based questionnaires containing information about sex, age, disease progression, patient-management, and number of BACM cases treated previously. We compared IA-BACM cases with influenza cases from the German virologic sentinel surveillance system for influenza.

RESULTS

We investigated 219 children with IA-BACM. They coincided with the curve of influenza B of the German virologic sentinel surveillance system for influenza. Median age was 7 years, 74% (160/216) of cases were male, median time between the onset of fever and onset of BACM-symptoms was 3 days lasting for a median of 4 days. Almost half of the affected children had presented at hospitals. One case with beginning renal impairment occurred, but the patient recovered completely. Most reporting physicians had not seen BACM-patients previously. Multivariable analysis showed IA-BACM's strong association with influenza B, male sex, and age between 6 and 9 years.

CONCLUSIONS

Influenza B caused a large BACM outbreak in Germany. Onset of BACM symptoms followed shortly after the onset of influenza symptoms. The course of this disease was almost exclusively mild and self-limiting. Diagnosis of this rare but distinct clinical entity by the alert physician can spare the patient potentially unneeded invasive testing and hospital admission.

Benign acute myositis associated with H1N1 influenza A virus infection

We report the clinical and laboratory features of four children with benign acute myositis observed during the current outbreak of the novel H1N1 influenza A virus. Our findings were similar to those of previous reports for benign acute myositis associated with seasonal influenza. No patients needed oseltamivir, and all of them showed quick recovery without recurrences. In the current H1N1 influenza virus pandemic, the diagnosis of benign acute myositis must be suspected in those children with flu symptoms and difficulty to walk, taking this into account might help avoiding unnecessary studies.

Novel H1N1-associated rhabdomyolysis leading to acute renal failure

The WHO recently declared that the novel influenza H1N1 virus was responsible for the 2009 flu pandemic. As the virus continues to spread globally and affect more individuals, more complications of infection with this virus are being recognized. To our knowledge, we report the first case of H1N1-induced rhabdomyolysis leading to acute renal failure in an adult. This case highlights the importance of recognizing a significant extrapulmonary complication of H1N1 infection.

A case of benign acute childhood myositis associated with influenza A (H1N1) virus infection

Benign acute childhood myositis (BACM) is a rare transient condition usually occurring at the early convalescent phase of a viral upper respiratory tract illness, normally influenza A, and, more frequently, influenza B infection. It is characterized by acute-onset difficulty in walking as a result of severe bilateral calf pain and by elevated muscle enzymes including creatinine kinase. It is self-limiting because there is rapid full recovery usually within 1 week. We describe the first case of BACM in association with the new pandemic influenza A (H1N1) virus infection in an 11-year-old boy from Cyprus. The child had the typical clinical and laboratory characteristics of this clinical syndrome. Prompt diagnosis of this clinical entity is essential to prevent unnecessary investigations and therapeutic interventions and to reassure the patient and parents of the excellent prognosis.

Clinical features of children infected with different strains of influenza B in southern Taiwan

BACKGROUND

This study was designed to determine the clinical characteristics of children infected with different strains of influenza B viruses isolated in southern Taiwan. The clinical features were compared with influenza A infection occurring in the same period.

METHODS

All children enrolled in the study had laboratory-confirmed infection with influenza A or B viruses. Influenza B speciation was performed by RNA extraction, cDNA synthesis, and amplification by polymerase chain reaction and sequencing. Demographic data, clinical findings, diagnoses, and outcomes were obtained.

RESULTS

During the study period, 163 strains of influenza A and 118 strains of influenza B were isolated. The Yamagata-like strains were most prevalent in 2001. New reassortant strains were identified since 2002 and became predominant in 2005 and 2006. Children with influenza B were more likely than those with influenza A to be diagnosed as upper respiratory tract infection, myositis, and gastroenteritis (P < 0.05). Children infected with Yamagata-like strains were more likely to develop lower respiratory tract infection (P < 0.05) and accounted for all cases of invasive disease. Children infected with the Victoria-like group had the longest hospital stays associated with severe bacterial superinfection.

CONCLUSIONS

Currently new reassortant influenza B viruses are the predominant strains circulating in southern Taiwan. There is considerable similarity of clinical features between influenza A and B in children. The Yamagata-like strains were associated with more invasive infections. Continuous influenza virus surveillance is essential particularly in Taiwan where pandemic strains tend to appear earlier than in other countries.

Bacterial, fungal, parasitic, and viral myositis

Infectious myositis may be caused by a broad range of bacterial, fungal, parasitic, and viral agents. Infectious myositis is overall uncommon given the relative resistance of the musculature to infection. For example, inciting events, including trauma, surgery, or the presence of foreign bodies or devitalized tissue, are often present in cases of bacterial myositis. Bacterial causes are categorized by clinical presentation, anatomic location, and causative organisms into the categories of pyomyositis, psoas abscess, Staphylococcus aureus myositis, group A streptococcal necrotizing myositis, group B streptococcal myositis, clostridial gas gangrene, and nonclostridial myositis. Fungal myositis is rare and usually occurs among immunocompromised hosts. Parasitic myositis is most commonly a result of trichinosis or cystericercosis, but other protozoa or helminths may be involved. A parasitic cause of myositis is suggested by the travel history and presence of eosinophilia. Viruses may cause diffuse muscle involvement with clinical manifestations, such as benign acute myositis (most commonly due to influenza virus), pleurodynia (coxsackievirus B), acute rhabdomyolysis, or an immune-mediated polymyositis. The diagnosis of myositis is suggested by the clinical picture and radiologic imaging, and the etiologic agent is confirmed by microbiologic or serologic testing. Therapy is based on the clinical presentation and the underlying pathogen.

Benign acute childhood myositis: an unusual cause of calf pain

We present a 17-year-old boy with benign acute childhood myositis (BACM) who presented with acute onset of right calf pain, swelling, and difficulty walking. The MR findings are reviewed. MR may be useful in diagnosing BACM and in differentiating it from other causes of myositis.

Severe influenza B myocarditis and myositis

OBJECTIVE

To report an influenza B infection with associated myocarditis and severe skeletal myositis.

DESIGN

Case report.

SETTING

Cardiac intensive care unit in a university-affiliated children's hospital.

PATIENT

A 4-yr-old girl.

RESULTS

The patient was successfully supported with extracorporeal membrane oxygenation for profound myocardial dysfunction and a combination of plasmapheresis and continuous venovenous hemodialysis for rhabdomyolysis and acute renal failure.

CONCLUSIONS

This case provides a reminder that patients presenting with viral illness or myoglobinuria accompanied by renal failure, with or without associated myocarditis, may be demonstrating symptoms of influenza B.

Animal models of myositis

Current animal models of human myositis include spontaneous, induced, and transgenic models. Although it is clear that none of these models possesses all the features of the human diseases, they may provide insight into the pathophysiologic mechanisms, and possibly the therapy, of inflammatory muscle disease. Because the human IIMs are phenotypically heterogeneous, but may be divided into more homogeneous subgroups based upon clinical or serologic features, it is possible that different pathogeneses are involved in different subgroups. It is unlikely that any single model would reproduce all features of the human disease. It may be possible, however, to gain insight into some subgroups of the human disease if certain animal models faithfully reproduce one or more subtypes or aspects of the IIMs. Because immunogenetic risk factors, and exposure to certain environmental agents important in triggering myositis in genetically susceptible persons, may be necessary components for human disease induction, transgenic approaches to humanizing murine immune systems and a better understanding of environmental risk factors will be productive avenues for future research. Additional investigations into the molecular basis of the human myositis syndromes and the pathogenesis of the spontaneous, induced, and transgenic animal models should ultimately allow for better understanding and therapy of these diseases.