Myopathy associated with neuromyelitis optica spectrum disorders

A rare adverse effect in inebilizumab therapy for neuromyelitis optica spectrum disorder: a case report

Inebilizumab is one of the monoclonal antibodies approved as maintenance therapy for aquaporin-4 immunoglobulin G-seropositive neuromyelitis optica spectrum disorder (NMOSD). It is a humanized monoclonal antibody targeting cluster of differentiation 19 (CD19). Common adverse reactions include urinary tract infections, nasopharyngitis, arthralgia, infusion reactions, headaches and a decrease in immunoglobulin levels. Here, we present a case of an NMOSD patient who experienced transient hyperCKaemia after the use of inebilizumab. The adverse reactions of this very rare monoclonal antibody drug improved after discontinuation.

Assessing the Role of Aquaporin 4 in Skeletal Muscle Function

Water transport across the biological membranes is mediated by aquaporins (AQPs). AQP4 and AQP1 are the predominantly expressed AQPs in the skeletal muscle. Since the discovery of AQP4, several studies have highlighted reduced AQP4 levels in Duchenne muscular dystrophy (DMD) patients and mouse models, and other neuromuscular disorders (NMDs) such as sarcoglycanopathies and dysferlinopathies. AQP4 loss is attributed to the destabilizing dystrophin-associated protein complex (DAPC) in DMD leading to compromised water permeability in the skeletal muscle fibers. However, AQP4 knockout (KO) mice appear phenotypically normal. AQP4 ablation does not impair physical activity in mice but limits them from achieving the performance demonstrated by wild-type mice. AQP1 levels were found to be upregulated in DMD models and are thought to compensate for AQP4 loss. Several groups investigated the expression of other AQPs in the skeletal muscle; however, these findings remain controversial. In this review, we summarize the role of AQP4 with respect to skeletal muscle function and findings in NMDs as well as the implications from a clinical perspective.

AQP4-IgG may cause muscle damage in patients with neuromyelitis optica spectrum disorder

BACKGROUND

Muscle damage has been found in patients with neuromyelitis optica spectrum disorder (NMOSD), but whether this damage is related to aquaporin-4 immunoglobulin G antibodies (AQP4-IgG) is uncertain. The aim of this study was to investigate the relationship between AQP4-IgG and muscle damage.

METHODS

From January 2009 to May 2019, we prospectively screened 1209 Chinese Han patients with acute transverse myelitis (ATM). Ultimately, we included 203 ATM patients in the cohort study and compared log serum creatine kinase (sCK) levels between positive and negative AQP4-IgG statuses.

RESULTS

Among all ATM patients, the mean log sCK levels of AQP4-IgG-positive patients were higher than those of AQP4-IgG-negative patients (4.46 ± 0.10 vs. 4.16 ± 0.06, p < 0.001). In addition, among ATM patients diagnosed with NMOSD, the mean log sCK levels of AQP4-IgG-positive patients were higher than those of AQP4-IgG-negative patients (4.46 ± 0.10 vs. 4.05 ± 0.13, p = 0.025). The number of extremely high sCK values (sCK values > 300 IU/L) was significantly higher in ATM patients positive for AQP4-IgG than in those negative for AQP4-IgG (p = 0.020). Furthermore, multivariable linear regression model analysis showed that male sex (coefficient [95% CI] = 0.548 [0.286, 0.809], p < 0.001), serum AQP4-IgG (coefficient [95% CI] = 0.462 [0.237, 0.687], p < 0.001), and combined connective tissue disease (CTD) (coefficient [95% CI] = -0.686 [-1.145, -0.226], p = 0.004) were independent predictors of log sCK levels.

CONCLUSIONS

Our study suggests that muscle damage in NMOSD patients may be associated with AQP4-IgG.

Serum Creatine Kinase in Patients with Neuromyelitis Optica Spectrum Disorder

OBJECTIVES

There have been reports of elevated serum creatine kinase (CK) and myopathy in patients with Neuromyelitis Optica Spectrum Disorder (NMOSD). Such findings have raised the possibility that myopathies may be a part of the spectrum of NMOSD. The incidence of elevated CK in NMOSD remains unknown. We sought to assess the potential association between hyperCKemia, myopathy, and NMOSD, and the potential role of screening for muscle involvement using serum CK.

METHODS

We reviewed records of all aquaporin 4 (AQP4) antibody-seropositive and seronegative NMOSD patients who had CK levels evaluated at two major academic medical centers.

RESULTS

Of 199 total NMOSD patients, CK levels were checked in 43, and elevated, on at least one occasion, in 4. In 1 patient, CK was elevated during an NMO exacerbation. A myopathic process occurring with NMOSD was suggested in 2 of 4 patients in the form of symptomatic complaint of myalgias and associated MRI signal change.

DISCUSSION

Unexplained hyperCKemia was found on one or more occasion in 4 of 43 tested NMOSD patients. Testing NMOSD patients for serum CK may reveal otherwise unsuspected myopathy. More formally powered, prospective assessment of the incidence and utility of CK in NMOSD is needed.

Pattern Recognition of the Multiple Sclerosis Syndrome

During recent decades, the autoimmune disease neuromyelitis optica spectrum disorder (NMOSD), once broadly classified under the umbrella of multiple sclerosis (MS), has been extended to include autoimmune inflammatory conditions of the central nervous system (CNS), which are now diagnosable with serum serological tests. These antibody-mediated inflammatory diseases of the CNS share a clinical presentation to MS. A number of practical learning points emerge in this review, which is geared toward the pattern recognition of optic neuritis, transverse myelitis, brainstem/cerebellar and hemispheric tumefactive demyelinating lesion (TDL)-associated MS, aquaporin-4-antibody and myelin oligodendrocyte glycoprotein (MOG)-antibody NMOSD, overlap syndrome, and some yet-to-be-defined/classified demyelinating disease, all unspecifically labeled under MS syndrome. The goal of this review is to increase clinicians’ awareness of the clinical nuances of the autoimmune conditions for MS and NMSOD, and to highlight highly suggestive patterns of clinical, paraclinical or imaging presentations in order to improve differentiation. With overlay in clinical manifestations between MS and NMOSD, magnetic resonance imaging (MRI) of the brain, orbits and spinal cord, serology, and most importantly, high index of suspicion based on pattern recognition, will help lead to the final diagnosis.

Supramolecular aggregation of aquaporin-4 is different in muscle and brain: correlation with tissue susceptibility in neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease of the central nervous system (CNS) caused by autoantibodies (NMO‐IgG) against the water channel aquaporin‐4 (AQP4). Though AQP4 is also expressed outside the CNS, for example in skeletal muscle, patients with NMO generally do not show clinical/diagnostic evidence of skeletal muscle damage. Here, we have evaluated whether AQP4 supramolecular organization is at the basis of the different tissue susceptibility. Using immunofluorescence we found that while the sera of our cohort of patients with NMO gave typical perivascular staining in the CNS, they were largely negative in the skeletal muscle. This conclusion was obtained using human, rat and mouse skeletal muscle including the AQP4‐KO mouse. A biochemical analysis using a new size exclusion chromatography approach for AQP4 suprastructure fractionation revealed substantial differences in supramolecular AQP4 assemblies and isoform abundance between brain and skeletal muscle matching a lower binding affinity of NMO‐IgG to muscle compared to the brain. Super‐resolution microscopy analysis with g‐STED revealed different AQP4 organization in native tissues, while in the brain perivascular astrocyte endfoot membrane AQP4 was mainly organized in large interconnected and raft‐like clusters, in the sarcolemma of fast‐twitch fibres AQP4 aggregates often appeared as small, relatively isolated linear entities. In conclusion, our results provide evidence that AQP4 supramolecular structure is different in brain and skeletal muscle, which is likely to result in different tissues susceptibility to the NMO disease.

Muscle damage in patients with neuromyelitis optica spectrum disorder

Objective:

Increasing evidence has shown that skeletal muscle damage plays a role in neuromyelitis optica spectrum disorder (NMOSD). The objective of this study was to compare the serum creatine kinase (sCK) levels in NMOSD patients with different clinical statuses.

Methods:

In the observational study, levels of sCK were measured during the acute and stable phases for patients with NMOSD and healthy controls (HCs).

Results:

We enrolled 168 patients with NMOSD (female:male ratio, 153:15; age: 43.9 ± 13.1 years) in the acute phase, and blood samples were collected from 85 of the patients with NMOSD during both acute and stable phases to determine the sCK levels. The mean log sCK levels of the patients with NMOSD in the acute phase were higher (4.51 ± 1.17, n = 85) than those of the patients with NMOSD in the stable phase (3.85 ± 0.81, n = 85, p = 0.000). Furthermore, the log sCK levels of the patients with NMOSD in the stable phase were lower than those of the HCs (4.31 ± 0.39, n = 200, p = 0.000). In patients with sCK levels within the normal limits, these differences were also observed (p < 0.05). In the multivariable linear regression model performed for the patients with NMOSD in the acute phase, it suggested that a higher estimated glomerular filtration rate (p = 0.026), patients with the core clinical characteristics of optic neuritis (p = 0.005), and serum anti-SSA positivity (p = 0.019) predicted lower log sCK levels.

Conclusions:

Muscle damage occurs in patients with NMOSD and is aggravated during the acute phase.

The link between morphology and complement in ocular disease

The complement system is a vital component of the immune-priveliged human eye that is always active at a low-grade level, preventing harmful intraocular injuries caused by accumulation of turnover products and controlling pathogens to preserve eye homeostasis and vision. The complement system is a double-edged sword that is essential for protection but may also become harmful and contribute to eye pathology. Here, we review the evidence for the involvement of complement system dysregulation in age-related macular degeneration, glaucoma, uveitis, and neuromyelitis optica, highlighting the relationship between morphogical changes and complement system protein expression and regulation in these diseases. The potential benefits of complement inhibition in age-related macular degeneration, glaucoma, uveitis, and neuromyelitis optica are abundant, as are those of further research to improve our understanding of complement-mediated injury in these diseases.

Complexity and wide range of neuromyelitis optica spectrum disorders: more than typical manifestations

Neuromyelitis optica (NMO), considered to be mediated by autoantibodies, often cause severely disabling disorders of the central nervous system, and predominantly cause optic nerve damage and longitudinally extensive transverse myelitis. Remarkable progress has been made in deciphering NMO pathogenesis during the past decade. In 2015, the International Panel for NMO Diagnosis proposed the unifying term "NMO spectrum disorders" (NMOSD) and the updated NMOSD criteria reflects a wide range of disease and maintains reasonable specificity. Moreover, cumulative findings have indicated that NMOSD are frequently associated with multiple autoimmune diseases, thereby presenting complex clinical symptoms that make this disease more difficult to recognize. Notably, most neurologists do not heed these symptoms or comorbid conditions in patients with NMOSD. Whereas previous reviews have focused on pathogenesis, treatment, and prognosis in NMOSD, we summarize the present knowledge with particular emphasis on atypical manifestations and autoimmune comorbidities in patients with NMOSD. Furthermore, we emphasized the identification of these atypical characteristics to enable a broader and better understanding of NMOSD, and improve early accurate diagnosis and therapeutic decision making.