A pediatric patient with myopathy associated with antibodies to a signal recognition particle

Anti-SRP myositis: a diagnostic and therapeutic challenge

BACKGROUND

Anti-signal recognition protein (anti-SRP) myopathy is a rare idiopathic inflammatory myopathy in children. Herein, a 3-year-old patient with severe anti-SRP myopathy showing a rapidly progressive disease course is presented in order to increase the awareness of pediatricians about idiopathic inflammatory myopathies.

CASE PRESENTATION

A previously healthy 3-year-old girl presented with progressive symmetrical proximal muscle weakness that caused difficulty in climbing stairs for two months prior to evaluation, and a marked elevation of the serum creatine kinase levels. A skeletal muscle biopsy revealed necrotic and regenerating processes, with mild inflammatory changes. Myositis-specific and associated autoantibodies tested by the immunoblot method were positive for anti-SRP. Pulse corticosteroid, intravenous immunoglobulin, and methotrexate were administered. However, muscle weakness progressed, respiratory distress and dysphagia developed. Rituximab was initiated. While on rituximab treatment, she was able to walk independently and muscle enzymes were within normal range at the 15th month of diagnosis.

CONCLUSION

Early diagnosis of patients with anti-SRP myositis is important to control inflammation and prevent disease progression and complications. To our knowledge, our patient is the youngest case reported in the literature and was successfully treated with rituximab added to conventional therapy.

Plasma Exchange in Anti-Signal Recognition Particle Myopathy: A Systematic Review and Combined Analysis of Patient Individual Data

Anti-signal recognition particle myopathy (anti-SRP myopathy) is a rare subtype of immune-mediated inflammatory myopathy characterized by muscle weakness and anti-SRP autoantibodies. Although plasma exchange (PE) is used in severe cases, its role remains unclear. A systematic review was conducted following PRISMA guidelines, identifying 23 patients with anti-SRP myopathy treated with PE. Data on demographics, clinical features, laboratory findings, treatments, and outcomes were analyzed combining individual patient data if available. Sixteen (69.6%) patients were male, with muscle weakness as the predominant symptom in 100% of cases. After PE, most patients showed improvement in symptoms, and the proportion of patients with muscle weakness was reduced (p = 0.001). Relapse occurred in 17.4% of the cases. The incidence of adverse events was low (8.7%). Despite limitations, including a small sample size and heterogeneous data, our systematic review suggests that PE may be effective in inducing remission and controlling symptoms in anti-SRP myopathy, particularly in severe cases. Since evidence on PE in anti-SRP myopathy is limited, further research, including prospective multicenter studies, is warranted to understand better its efficacy and safety and establish its role in treatment algorithms.

Pediatric immune-mediated necrotizing myopathy

Immune-mediated necrotizing myopathy (IMNM) is a type of inflammatory myopathy. Most patients with IMNM produce anti-3-hydroxy-3-methylglutaryl coenzyme A reductase or anti-signal-recognition particle autoantibodies. IMNM is much rarer in children than in adults. We conducted this mini review focusing on pediatric IMNM to present current evidence regarding its epidemiology, clinical characteristics, diagnosis, and treatment. Our findings indicate that pediatric IMNM often causes severe muscle weakness and is refractory to corticosteroids alone. Furthermore, delayed diagnosis is common because of the clinicopathological similarity between IMNM and inherited myopathy. Raising awareness regarding pediatric IMNM may facilitate early diagnosis and effective treatment.

Clinical Course, Myopathology and Challenge of Therapeutic Intervention in Pediatric Patients with Autoimmune-Mediated Necrotizing Myopathy

(1) Background: Immune–mediated necrotizing myopathy (IMNM) is a rare form of inflammatory muscle disease which is even more rare in pediatric patients. To increase the knowledge of juvenile IMNM, we here present the clinical findings on long-term follow-up, myopathological changes, and therapeutic strategies in two juvenile patients. (2) Methods: Investigations included phenotyping, determination of antibody status, microscopy on muscle biopsies, MRI, and response to therapeutic interventions. (3) Results: Anti-signal recognition particle (anti-SRP54) and anti- 3-hydroxy-3-methylglutarly coenzyme A reductase (anti-HMGCR) antibodies (Ab) were detected in the patients. Limb girdle presentation, very high CK-levels, and a lack of skin rash at disease-manifestation and an absence of prominent inflammatory signs accompanied by an abnormal distribution of α-dystroglycan in muscle biopsies initially hinted toward a genetically caused muscle dystrophy. Further immunostaining studies revealed an increase of proteins involved in chaperone-assisted autophagy (CASA), a finding already described in adult IMNM-patients. Asymmetrical muscular weakness was present in the anti-SRP54 positive Ab patient. After initial stabilization under therapy with intravenous immunoglobulins and methotrexate, both patients experienced a worsening of their symptoms and despite further therapy escalation, developed a permanent reduction of their muscle strength and muscular atrophy. (4) Conclusions: Diagnosis of juvenile IMNM might be complicated by asymmetric muscle weakness, lack of cutaneous features, absence of prominent inflammatory changes in the biopsy, and altered α-dystroglycan.

Use of Rescue Therapy with IVIG or Cyclophosphamide in Juvenile Myositis

PURPOSE OF REVIEW

This review aims to present the literature available to date on the use of intravenous immunoglobulin and cyclophosphamide for juvenile patients with inflammatory myopathies, to evaluate the strength of the evidence so far for both these medications, and to reach conclusions about their efficacy.

RECENT FINDINGS

Juvenile idiopathic inflammatory myopathies, mainly represented by juvenile dermatomyositis (JDM), are rare diseases but quite debilitating for the patients. JDM is an autoimmune condition with predominantly muscle and skin involvement but also systemic features affecting the cardiovascular, respiratory, and gastrointestinal systems. The mainstay therapy is based on corticosteroids and methotrexate, but often other therapeutic alternatives are sought for patients with severe or refractory disease. The rarity of these conditions makes research for new medications even more challenging. Innovative trial designs or statistical methods can be used to emulate a randomized study and investigate drug effectiveness. Despite the lack of Level I evidence on the use and efficacy of intravenous immunoglobulin and cyclophosphamide, their use is advocated by a substantial number of case reports and case series as well as analyses using marginal structural models.

Effective induction therapy for anti-SRP associated myositis in childhood: A small case series and review of the literature

BACKGROUND

Anti-Signal Recognition Particle associated myopathy is a clinically and histopathologically distinct subgroup of Juvenile Idiopathic Inflammatory Myositis, which is under-recognised in children and fails to respond to conventional first line therapies. We present three cases where remission was successfully induced using combination therapy with intensive rehabilitation.

CASE PRESENTATIONS

Three new patients are reported. All 3 cases presented with profound, rapid-onset, proximal myopathy and markedly raised CK, but no rash. Histology revealed a destructive myopathy characterized by scattered atrophic and necrotic fibres with little or no inflammatory infiltrate. All 3 patients responded to induction with cyclophosphamide, IVIG and rituximab, in conjunction with intensive physiotherapy and methotrexate as the maintenance agent. Our patients regained near-normal strength (MMT > 70/80), in contrast with the current literature where >50% of cases reported severe residual weakness. A literature search on paediatric anti-SRP myositis was performed to June 2016; PubMed was screened using a combination of the following terms: signal recognition particle, autoantibodies, antibodies, myositis, muscular diseases, skeletal muscle, childhood, paediatric, juvenile. Articles in a foreign language were excluded. Nine case studies were found.

CONCLUSION

This paper supports the hypothesis that anti-SRP myositis is distinct from other JIIM. It is an important differential to JDM and should be considered where there is severe weakness without rash or if highly elevated muscle enzymes (CK > 10,000 U/l) are found. Early identification is essential to initiate aggressive medical and physical therapy. Greater international collaboration and long-term follow-up data is needed to establish the most effective treatment strategy for this rare group of patients.

Chronic Myopathy Associated With Anti-Signal Recognition Particle Antibodies Can Be Misdiagnosed As Facioscapulohumeral Muscular Dystrophy

OBJECTIVES

To report cases of chronic autoimmune necrotizing myopathy with anti-signal recognition particle antibodies (anti-SRP myopathy) initially misdiagnosed as muscular dystrophy, in particular, facioscapulohumeral muscular dystrophy (FSHD).

METHODS

Medical records of patients with anti-SRP myopathy in our institution were retrospectively reviewed.

RESULTS

All 6 patients were initially diagnosed with muscular dystrophy because of the long-term clinical course and lack of inflammation on biopsy; 5 were diagnosed with FSHD based on a winged scapula. However, the following features suggested an alternative diagnosis, leading to anti-SRP antibody measurement: (1) lack of family history, (2) lack of facial involvement and asymmetry, (3) prominent dysphagia, and (4) profuse spontaneous activities on needle electromyography. All patients showed improvement with immunomodulating therapy.

CONCLUSIONS

Anti-SRP antibody measurement should be considered in patients diagnosed with FSHD if they present with diagnostic hallmarks of anti-SRP myopathy listed above, to avoid oversight of this potentially treatable disorder.