AB1078 USE OF MYOSITIS SPECIFIC AUTOANTIBODIES TEST ACROSS A LARGE NHS HOSPITAL TRUST

Background:

The immunology laboratory at Barts Health supports a large clinical myopathy service, providing blood tests for myositis-specific autoantibodies (MSA) by a commercial line immunoblot panel for Jo1, PL7, PL12, SRP, Mi2, Ku, PM-Scl and Scl-70.

As Idiopathic Inflammatory Myositis (IIM) disease subtype definitions have evolved from the 1975 Bohan & Peter criteria, the discovery of new antibodies has proven useful in the hands of neuromuscular clinicians whose patients have a high pre-test probability of disease. Ready availability of the test has led to increased demand from:

Objectives:

Determine the frequency of MSA requests from different departments.

To investigate the possibility of rejecting requests for MSAs at the laboratory in the absence of an elevated creatine kinase (CK), a hallmark of muscle damage associated with myositis (1).

Methods:

MSA were measured by a commercial line blot (Bluediver) which included Jo-1, PL-7, PL-12, Mi-2, Ku, SRP-54 and PM-Scl-100. Demographics and results for all MSA requested between September 2017 and November 2019 were pulled from laboratory records, together with CK results (if performed). CK was interpreted as low, normal or elevated according to reference ranges of 25-200 U/L (female) or 40-320 U/L (male).

Results:

597 tests were performed between 2017 and 2019. In total 59/597 (10%) were positive for the audited antibodies (Table 1). General Practitioner (GP) requests accounted for 41/597 (6.9%) tests, internal 464/597 (78%) and external 82/597 (14%). External requests were the most frequently positive at 10/82 (12%), internal requests 46/464 (10%), and GP requests only 3/41 (7%) of the time. Of all internal requesting sources, Respiratory accounted for the largest number at 108/597 (18%), followed by neurology with 85/597 (14%) (Figure 1). GPs constituted the 4thlargest source of requests.

Table 1.Positive on polymyositis screen% positivityAll tests597Total599.9%Jo-140.7%PL-720.3%PL-1250.8%SRP-54101.7%Mi-240.7%Ku30.5%PM-Scl 100254.2%Scl-7071.2%Figure 1.

MSAs had an associated CK result in 75% of internal and 12% of GP requests. A cohort of 17 patients had positive MSAs (3 x SRP, 1 x PL-7, 1 x Jo-1, 2 x Mi-2, 1 x Ku, 8 x PM-Scl100 and 1 x Scl-70) with normal CK.

Of the 41 GP requests, MSA had been requested by the lab on the basis of ANA pattern for 33 (80%) of them, 3 of which were positive (2 x Scl-70, 1 x SRP-54).

Conclusion:

Demand for MSA from the Respiratory department (screening for ILD) currently exceeds demand from Neurology and from Rheumatology. In the GP cohort, 33 requests (80% of GPs, 5% of all requests) were generated by the laboratory.

A cohort of patients with normal CK results had a positive MSA, implying CK alone cannot be used to limit test access. Interestingly, 10 positive results had no CK requested implying they were not being investigated for myositis.

Further work is needed to determine the specificity and sensitivity of these antibodies for patients with clinically defined myositis, and the appropriateness of allowing the test to be applied in the absence of any clinical evidence of IIM.

The findings of this audit need to be further extended to look at other myositis including other anti-synthetases, HMGCoAR, MDA5, TIF-1γ, NPX-2.

References:

[1]Dalakas MC, Hohlfeld R (2003) Polymyositis and dermatomyositis. Lancet 362:971–982

Disclosure of Interests:

None declared

The histopathological spectrum of malignant hyperthermia and rhabdomyolysis due to RYR1 mutations

Objective

The histopathological features of malignant hyperthermia (MH) and non-anaesthetic (mostly exertional) rhabdomyolysis (RM) due to RYR1 mutations have only been reported in a few cases.

Methods

We performed a retrospective multi-centre cohort study focussing on the histopathological features of patients with MH or RM due to RYR1 mutations (1987–2017). All muscle biopsies were reviewed by a neuromuscular pathologist. Additional morphometric and electron microscopic analysis were performed where possible.

Results

Through the six participating centres we identified 50 patients from 46 families, including patients with MH (n = 31) and RM (n = 19). Overall, the biopsy of 90% of patients showed one or more myopathic features including: increased fibre size variability (n = 44), increase in the number of fibres with internal nuclei (n = 30), and type I fibre predominance (n = 13). Abnormalities on oxidative staining, generally considered to be more specifically associated with RYR1-related congenital myopathies, were observed in 52%, and included unevenness (n = 24), central cores (n = 7) and multi-minicores (n = 3). Apart from oxidative staining abnormalities more frequently observed in MH patients, the histopathological spectrum was similar between the two groups. There was no correlation between the presence of cores and the occurrence of clinically detectable weakness or presence of (likely) pathogenic variants.

Conclusions

Patients with RYR1-related MH and RM exhibit a similar histopathological spectrum, ranging from mild myopathic changes to cores and other features typical of RYR1-related congenital myopathies. Suggestive histopathological features may support RYR1 involvement, also in cases where the in vitro contracture test is not informative.

Electronic supplementary material

The online version of this article (10.1007/s00415-019-09209-z) contains supplementary material, which is available to authorized users.

Leprosy: a 'common' and curable cause of peripheral neuropathy with skin lesions

Leprosy (or Hansen's disease) is a curable chronic infectious disease caused by the acid-fast bacillus Mycobacterium leprae. While leprosy remains one of the most common causes of neuropathy worldwide, its rarity in the UK means that many doctors are unfamiliar with the typical clinical features. This is problematic because early recognition and treatment is vital in order to minimise disease-related complications such as nerve injury. We describe a 75-year-old man who presented with multiple mononeuropathy (mononeuritis multiplex, particularly affecting the ulnar nerves) and typical granulomatous skin lesions, in whom the diagnosis was made on the basis of skin biopsy. We highlight the clinical features, investigations and treatment of the patient, and provide information about the epidemiology and pathogenesis of leprosy.

Mutations in RYR1 are a common cause of exertional myalgia and rhabdomyolysis

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene are a common cause of neuromuscular disease, ranging from various congenital myopathies to the malignant hyperthermia (MH) susceptibility trait without associated weakness. We sequenced RYR1 in 39 unrelated families with rhabdomyolysis and/or exertional myalgia, frequent presentations in the neuromuscular clinic that often remain unexplained despite extensive investigations. We identified 9 heterozygous RYR1 mutations/variants in 14 families, 5 of them (p.Lys1393Arg; p.Gly2434Arg; p.Thr4288_Ala4290dup; p.Ala4295Val; and p.Arg4737Gln) previously associated with MH. Index cases presented from 3 to 45 years with rhabdomyolysis, with or without exertional myalgia (n=12), or isolated exertional myalgia (n=2). Rhabdomyolysis was commonly triggered by exercise and heat and, less frequently, viral infections, alcohol and drugs. Most cases were normally strong and had no personal MH history. Inconsistent additional features included heat intolerance, and cold-induced muscle stiffness. Muscle biopsies showed mainly subtle changes. Familial RYR1 mutations were confirmed in relatives with similar or no symptoms. These findings suggest that RYR1 mutations may account for a substantial proportion of patients presenting with unexplained rhabdomyolysis and/or exertional myalgia. Associated clinico-pathological features may be subtle and require a high degree of suspicion. Additional family studies are paramount in order to identify potentially MH susceptible relatives.

Mutations in all five exons of SOD-1 may cause ALS

Eight of 38 patients (21%) with familial and 5 of 175 patients (3%) with sporadic amyotrophic lateral sclerosis (ALS) had missense mutations in the SOD-1 gene. Two novel mutations were identified. One in exon 4 substituting leucine with phenylalanine (L84F) in a familial patient and the second in exon 3 at substituting glycine with serine (G72S) in an "apparently" sporadic patient. Over 60 point mutations have now been described in all five exons of SOD-1, involving 43 of the 153 residues. Hypotheses about the toxic role of mutant SOD-1 in the pathogenesis of ALS must account for this molecular diversity.

Familial amyotrophic lateral sclerosis. Molecular pathology of a patient with a SOD1 mutation

We report the clinical, genetic, and neuropathologic findings in a patient with rapidly progressive familial amyotrophic lateral sclerosis (ALS). We detected a point mutation at codon 48 of the Cu/Zn superoxide dismutase gene (SOD1) leading to a substitution of histidine by glutamine in the copper-binding domain. The histopathologic features are consistent with those described in rapidly progressive sporadic ALS and do not support claims that sporadic and familial disease are different pathologic entities. Neurofilamentous accumulations, hyaline, and ubiquitinated inclusions were present in the motor cortex, brainstem, and anterior horn cells, but there was no evidence of abnormal SOD1 immunoreactivity. This confirms that the cytoskeletal pathology specific to ALS is secondary to an unknown biochemical disturbance caused by mutant SOD1 molecules and not its toxic accumulation.