Transthyretin V122I amyloidosis with clinical and histological evidence of amyloid neuropathy and myopathy

Prevalence and significance of extracardiac uptake on pyrophosphate imaging in the SCAN-MP study: the first 379 cases

INTRODUCTION

Technetium-labeled bone-avid radiotracers can be used to diagnose transthyretin cardiac amyloidosis (ATTR-CA). Extracardiac uptake of technetium pyrophosphate (Tc-99m PYP) in this context has not been extensively explored and its significance is not well characterized. We assessed extracardiac Tc-99m PYP uptake in individuals undergoing nuclear scintigraphy and the extent of clinically actionable findings.

METHODS

The Screening for Cardiac Amyloidosis with Nuclear Imaging in Minority Populations (SCAN-MP) study utilizes Tc-99m PYP imaging to identify ATTR-CA in self-identified Black and Caribbean Hispanic participants ≥ 60 years old with heart failure. We characterized the distribution of extracardiac uptake, including stratification of findings by timing of scan (1 hour vs 3 hours after Tc-99m PYP administration) and noted any additional testing in these subjects.

RESULTS

Of 379 participants, 195 (51%) were male, 306 (81%) Black race, and 120 (32%) Hispanic ethnicity; mean age was 73 years. Extracardiac Tc-99m PYP uptake was found in 42 subjects (11.1%): 21 with renal uptake only, 14 with bone uptake only, 4 with both renal and bone uptake, 2 with breast uptake, and 1 with thyroid uptake. Extracardiac uptake was more common in subjects with Tc-99m PYP scans at 1 hour (23.8%) than at 3 hours (6.2%). Overall, four individuals (1.1%) had clinically actionable findings.

CONCLUSION

Extracardiac Tc-99m PYP uptake manifested in about 1 in 9 SCAN-MP subjects but was clinically actionable in only 1.1% of cases.

Phenotypes Associated With the Val122Ile, Leu58His, and Late-Onset Val30Met Variants in Patients With Hereditary Transthyretin Amyloidosis

BACKGROUND AND OBJECTIVES

Hereditary transthyretin amyloidosis (hATTR) is a rare autosomal dominant systemic disease with variable penetrance and heterogeneous clinical presentation. Several effective treatments can reduce mortality and disability, though diagnosis remains challenging, especially in the United States where disease is nonendemic. Our aim is to describe the neurologic and cardiac characteristics of common US ATTR variants V122I, L58H, and late-onset V30M at presentation.

METHODS

We conducted a retrospective case series of patients with a new diagnosis of ATTRv between January 2008 and January 2020 to characterize features of prominent US variants. The neurologic (examination, EMG, and skin biopsy), cardiac (echo), and laboratory assessments (pro b-type natriuretic peptide [proBNP] and reversible neuropathy screens) are described.

RESULTS

A total of 56 patients with treatment-naïve ATTRv with symptoms/signs of peripheral neuropathy (PN) or cardiomyopathy and confirmatory genetic testing presenting with Val122Ile (N = 31), late-onset Val30Met (N = 12), and Leu58His ATTRv (N = 13) were included. The age at onset and sex distributions were similar (V122I: 71.5 ± 8.0, V30M: 64.8 ± 2.6, and L58H: 62.4 ± 9.8 years; 26, 25, 31% female). Only 10% of patients with V122I and 17% of patients with V30M were aware of an ATTRv family history, while 69% of patients with L58H were aware. PN was present in all 3 variants at diagnosis (90%, 100%, and 100%), though neurologic impairment scores differed: V122I: 22 ± 16, V30M: 61 ± 31, and L58H: 57 ± 25. Most points (deficits) were attributed to loss of strength. Carpal tunnel syndrome (CTS) and a positive Romberg sign were common across all groups (V122I: 97%, 39%; V30M: 58%, 58%; and L58H: 77%, 77%). ProBNP levels and interventricular septum thickness were highest among patients with V122I (5,939 ± 962 pg/mL, 1.70 ± 0.29 cm), followed by V30M (796 ± 970 pg/mL, 1.42 ± 0.38 cm) and L58H (404 ± 677 pg/mL, 1.23 ± 0.36 cm). Atrial fibrillation was present among 39% of cases with V122I and only 8% of cases with V30M and L58H. Gastrointestinal symptoms were rare (6%) among patients with V122I and common in patients with V30M (42%) and L58H (54%).

DISCUSSION

Important clinical differences exist between ATTRv genotypes. While V122I is perceived to be a cardiac disease, PN is common and clinically relevant. Most patients with V30M and V122I were diagnosed de novo and therefore require clinical suspicion for diagnosis. A history of CTS and a positive Romberg sign are helpful diagnostic clues.

99m Technetium-pyrophosphate bone scan: A potential biomarker for the burden of transthyretin amyloidosis in skeletal muscle: A preliminary study

INTRODUCTION/AIMS

Transthyretin amyloidosis (ATTR) proteins can infiltrate skeletal muscle and infrequently cause a myopathy. ^99m Technetium-pyrophosphate (^99m Tc-PYP) is a validated biomarker for cardiac involvement in variant and wild-type ATTR (ATTRv and ATTRwt, respectively). The aim of this study was to test the hypothesis that ^99m Tc-PYP is a biomarker for muscle burden of ATTR.

METHODS

Radioisotope uptake in the deltoid muscles of patients with ATTR was compared to uptake in control subjects without amyloidosis in a retrospective study. ^99m Tc-PYP scans were evaluated in 11 patients with ATTR (7 ATTRv, 4 ATTRwt) and 14 control subjects. Mean count (MC) values were measured in circular regions of interest (ROIs) 2.5-3.8 cm² in area. Tracer uptake was quantified in the heart, contralateral chest (CC), and deltoid muscles.

RESULTS

Tracer uptake was significantly higher over the deltoids and heart but not the CC, in patients with ATTR than in control subjects. MC values were 120.1 ± 43.7 (mean ± SD) in ATTR patients and 78.9 ± 20.4 in control subjects over the heart (p = 0.005), 73.3± 21.0 and 63.5 ± 14.4 over CC (p = 0.09), and 37.0 ± 11.7 and 26.0 ± 7.1 averaged over both deltoid muscles (p = 0.014).

DISCUSSION

^99m Tc-PYP is a potential biomarker for ATTR amyloid burden in skeletal muscle.

Neurological manifestations of hereditary transthyretin amyloidosis: a focus on diagnostic delays

BACKGROUND

The recent availability of disease-modifying therapies for hereditary transthyretin amyloid (ATTRv) amyloidosis warrants urgency for earlier diagnosis and timely identification of active disease state among genetic carriers.

METHODS

We reviewed clinical neurological data of all patients with ATTRv amyloidosis with initial visits at our amyloidosis centre between January 2016 and December 2018. We abstracted the signs and symptoms of neurological manifestations, as well as rates and patterns of diagnostic testing.

RESULTS

Of 92 patients with 19 different transthyretin (TTR) mutations, 66 and 36% had symptoms attributed to large-fibre and small-fibre neuropathy, respectively, compared to 75 and 66% with corresponding examination findings. Thirty-six patients with V122I ATTR mutation had asymptomatic polyneuropathy identified on neurological examination, eight without concurrent cardiac disease. Seventy-three percent of patients had symptoms of carpal tunnel syndrome (CTS), while 26% had dysautonomia. The average delays between the onset of symptoms of large fibre neuropathy (LFN) or CTS to ATTRv amyloidosis diagnosis were 2.9 and 6.7 years, respectively.

DISCUSSION

Our study found higher rates of polyneuropathy by examination than patient-reported symptoms, especially among those with V122I TTR amyloidosis, signalling asymptomatic polyneuropathy. Our findings suggest the need for routine neurological examinations and other testing for genetic carriers to achieve earlier identification of active disease state.

Quantitation of myocardial 99mTc-HMDP uptake with new SPECT/CT cadmium zinc telluride (CZT) camera in patients with transthyretin-related cardiac amyloidosis: Ready for clinical use?

BACKGROUND

The aim of this study was to investigate the feasibility of assessing absolute myocardial 99mTc-HMDP uptake in patients with suspected cardiac ATTR using SUV with a whole-body CZT SPECT-CT camera (DNM670CZT).

METHODS

Fifteen patients with suspected cardiac ATTR (Perugini ≥ 2) underwent a conventional 99mTc-HMDP planar imaging and a thoracic SPECT/CT using a DNM 670CZT. A control group consisted of 15 patients with negative scintigraphy (Perugini < 2). SUVmax (mg·L-1) and percentage of injected dose (%ID) were calculated in a cardiac volume of interest (VOI) encompassing the left ventricle. VOIs were also placed in the lung, the right pectoris major, and the sternum. A heart-to-lung SUVmax ratio (HLR) was calculated.

RESULTS

All ATTR patients demonstrated an increased cardiac HMDP SUVmax (12.2 ± 3.7 mg·L-1) vs controls (3.5 ± 1.2, P < .0001). Percentage of ID, pectoral uptake and HLR were significantly higher in the ATTR group (1.1 ± 0.3 vs 0.15 ± 0.8, P < .0001; 1.5 ± 0.3 vs 0.9 ± 0.3, P < .0001; 9.7 ± 3 vs 4.3 ± 2.2, P < .0001). Bone uptake was not statistically different between the two groups.

CONCLUSION

This study demonstrated the feasibility of quantitative 99mTc-HMDP SUVmax measurement using a whole-body SPECT/CT CZT camera in patients with suspected cardiac ATTR.

Progressive Multiple Mononeuropathy in a Patient With Familial Transthyretin Amyloidosis After Liver Transplantation

Valine 122 isoleucine (V122I) is the most common mutation associated with familial transthyretin-related amyloidosis (fATTR) in the metropolitan United States. V122I-related fATTR usually presents with cardiomyopathy. When polyneuropathy is encountered, it is usually mild, distal, and axonal in nature. Although liver transplantation improves survival for fATTR neuropathy patients, neuropathy may progress post liver transplantation because of the deposition of wild-type transthyretin. We report a patient with homozygous V122I mutation who presented with asymmetrical, upper limb predominant neuropathy rather early in his disease course, which progressed for a period of 5 years after liver transplantation before stabilization with the initiation of patisiran.

Current and Emerging Therapies for Hereditary Transthyretin Amyloidosis: Strides Towards a Brighter Future

The past few years have witnessed an unprecedented acceleration in the clinical development of novel therapeutic options for hereditary transthyretin amyloidosis. Recently approved agents and drugs currently under investigation not only represent a major breakthrough in this field but also provide validation of the therapeutic potential of innovative approaches, like RNA interference and CRISPR-Cas9-mediated gene editing, in rare inherited disorders. In this review, we describe the evolving therapeutic landscape for hereditary transthyretin amyloidosis and discuss how this highly disabling and fatal condition is turning into a treatable disease. We also provide an overview of the molecular mechanisms involved in transthyretin (TTR) amyloid formation and regression, to highlight how a deeper understanding of these processes has contributed to the identification of novel treatment targets. Finally, we focus on major areas of uncertainty and unmet needs that deserve further efforts to improve long-term patients' outcomes and allow for a brighter future.

Association of the transthyretin variant V122I with polyneuropathy among individuals of African ancestry

Hereditary transthyretin-mediated (hATTR) amyloidosis is an underdiagnosed, progressively debilitating disease caused by mutations in the transthyretin (TTR) gene. V122I, a common pathogenic TTR mutation, is found in 3-4% of individuals of African ancestry in the United States and has been associated with cardiomyopathy and heart failure. To better understand the phenotypic consequences of carrying V122I, we conducted a phenome-wide association study scanning 427 ICD diagnosis codes in UK Biobank participants of African ancestry (n = 6062). Significant associations were tested for replication in the Penn Medicine Biobank (n = 5737) and the Million Veteran Program (n = 82,382). V122I was significantly associated with polyneuropathy in the UK Biobank (odds ratio [OR] = 6.4, 95% confidence interval [CI] 2.6-15.6, p = 4.2 × 10-5), which was replicated in the Penn Medicine Biobank (OR = 1.6, 95% CI 1.2-2.4, p = 6.0 × 10-3) and Million Veteran Program (OR = 1.5, 95% CI 1.2-1.8, p = 1.8 × 10-4). Polyneuropathy prevalence among V122I carriers was 2.1%, 9.0%, and 4.8% in the UK Biobank, Penn Medicine Biobank, and Million Veteran Program, respectively. The cumulative incidence of common hATTR amyloidosis manifestations (carpal tunnel syndrome, polyneuropathy, cardiomyopathy, heart failure) was significantly enriched in V122I carriers compared with non-carriers (HR = 2.8, 95% CI 1.7-4.5, p = 2.6 × 10-5) in the UK Biobank, with 37.4% of V122I carriers having at least one of these manifestations by age 75. Our findings show that V122I carriers are at increased risk of polyneuropathy. These results also emphasize the underdiagnosis of disease in V122I carriers with a significant proportion of subjects showing phenotypic changes consistent with hATTR amyloidosis. Greater understanding of the manifestations associated with V122I is critical for earlier diagnosis and treatment.

Neuromuscular amyloidosis: Unmasking the master of disguise

Amyloidosis refers to an etiologically heterogeneous group of protein misfolding diseases, pathologically characterized by extracellular amyloid fibrils producing congophillic amorphous deposits in organs and tissues, which may lead to severe organ dysfunction and mortality. Clinical presentations vary and are often nonspecific, depending on what organs or tissues are affected. In systemic amyloidosis, the peripheral nervous system is commonly affected, whereas the skeletal muscles are only rarely involved. Immunoglobulin light chain (AL) amyloidosis and hereditary transthyretin (ATTRv) amyloidosis are the most frequent types of systemic amyloidosis involving the neuromuscular system. Localized amyloidosis can occur in skeletal muscle, so-called isolated amyloid myopathy. Amyloid neuropathy typically involves small myelinated and unmyelinated sensory and autonomic nerve fibers early in the course of the disease, followed by large myelinated fiber sensory and motor deficits. The relentlessly progressive nature with motor, painful sensory and severe autonomic dysfunction, profound weight loss, and systemic features are distinct characteristics of amyloid neuropathy. Amyloid myopathy presentation differs between systemic amyloidosis and isolated amyloid myopathy. Long-standing symptoms, distal predominant myopathy, markedly elevated creatine kinase level, and lack of peripheral neuropathy or systemic features are highly suggestive of isolated amyloid myopathy. In ATTR and AL amyloidosis, early treatment correlates with favorable outcomes. Therefore, awareness of these disorders and active screening for amyloidosis in patients with neuropathy or myopathy are crucial in detecting these patients in the everyday practice of neuromuscular medicine. Herein, we review the clinical manifestations of neuromuscular amyloidosis and provide a diagnostic approach to this disorder.

Genomic Screening Identifies Individuals at High Risk for Hereditary Transthyretin Amyloidosis

The TTR V142I variant associated with hereditary transthyretin amyloidosis (hATTR) is present in up to 4% of African American (AA) and 1% of Hispanic/Latinx (HL) individuals and increases risk for heart failure. Delayed and missed diagnoses could potentiate health disparities in these populations. We evaluated whether population-based genomic screening could effectively identify individuals at risk for hATTR and prompt initiation of risk management. We identified participants of the BioMe Biobank in New York City who received TTR V142I results through a pilot genomic screening program. We performed a retrospective medical record review to evaluate for the presence hATTR-related systemic features, uptake of recommended follow-up, and short-term outcomes. Thirty-two AA (N = 17) and HL (N = 15) individuals received a TTR V142I result (median age 57, 81% female). None had a previous diagnosis of hATTR. Eighteen (56%) had hATTR-related systemic features, including 4 (13%) with heart failure, 10 (31%) with carpal tunnel syndrome, and 10 (31%) with spinal stenosis. Eighteen (56%) pursued follow-up with a cardiologist within 8 months. One person received a diagnosis of hATTR. Thus, we found that the majority of V142I-positive individuals had hATTR-related systemic features at the time of result disclosure, including well-described red flags. Genomic screening can help identify hATTR risk and guide management early on, avoiding potential delays in diagnosis and treatment.

Cardiac Phenotypes in Hereditary Muscle Disorders: JACC State-of-the-Art Review

Hereditary muscular diseases commonly involve the heart. Cardiac manifestations encompass a spectrum of phenotypes, including both cardiomyopathies and rhythm disorders. Common biomarkers suggesting cardiomuscular diseases include increased circulating creatine kinase and/or lactic acid levels or disease-specific metabolic indicators. Cardiac and extra-cardiac traits, imaging tests, family studies, and genetic testing provide precise diagnoses. Cardiac phenotypes are mainly dilated and hypokinetic in dystrophinopathies, Emery-Dreifuss muscular dystrophies, and limb girdle muscular dystrophies; hypertrophic in Friedreich ataxia, mitochondrial diseases, glycogen storage diseases, and fatty acid oxidation disorders; and restrictive in myofibrillar myopathies. Left ventricular noncompaction is variably associated with the different myopathies. Conduction defects and arrhythmias constitute a major phenotype in myotonic dystrophies and skeletal muscle channelopathies. Although the actual cardiac management is rarely based on the cause, the cardiac phenotypes need precise characterization because they are often the only or the predominant manifestations and the prognostic determinants of many hereditary muscle disorders.

Increased Risk of Multiple Outpatient Surgeries in African-American Carriers of Transthyretin Val122Ile Mutation Is Modulated by Non-Coding Variants

Background: African-Americans (AAs) have a 3.5% carrier prevalence of Transthyretin (TTR) Val122Ile mutation (rs76992529), which is the genetic cause of a hereditary form of amyloidosis. Methods: We investigated the medical history of Val122Ile carriers and assessed the role of a non-coding variation in 4361 unrelated AAs. Results: We observed that the Ile122 allele was associated with a 6.8-fold increase in the odds of having 10 or more outpatient surgeries (p = 7.81 × 10⁻⁵). Stratifying the analysis by sex, the Ile122 allele was associated with a 15.2-fold increase in the odds of having 10 or more outpatient surgeries in men (p = 6.49 × 10⁻⁷). A similar sex difference was observed with respect to the association of Val122Ile with musculoskeletal and connective-tissue disorders in an independent cohort of British subjects (n = 361,194, p = 2.47 × 10⁻¹³; n_male = 167,020, p_male = 4.02 × 10⁻²⁴). In Val122Ile African-American carriers, we observed that haplotypes in the upstream region regulating TTR hepatic expression are associated with having 10 or more outpatient surgeries (p = 2.56 × 10⁻⁹). Conclusions: TTR Val122Ile showed a large effect with respect to an extreme phenotype identified in medical history that may be related to osteoarthritis, an early sign of the disease. Additionally, the non-coding variation appears to accelerate the negative consequences associated with Val122Ile mutation via TTR expression regulation.

Clinical Presentation, Diagnosis and Treatment of TTR Amyloidosis

Systemic amyloidosis can be hereditary or acquired with autosomal dominant mutations in the transthyretin gene (TTR) being the most common cause of hereditary amyloidosis. ATTRm amyloidosis is a multi-system disorder with cardiovascular, peripheral and autonomic nerve involvement that can be difficult to diagnose due to phenotypic heterogeneity. This review will focus on the neuropathic manifestations of ATTRm, the genotype-phenotype variability, the diagnostic approach and the recent therapeutic advances in this disabling condition.

Diagnosis of amyloid neuropathy

Systemic amyloidosis can be hereditary or acquired. The autosomal dominant hereditary transthyretin amyloidosis and the acquired light-chain amyloidosis, the result of a plasma cell dyscrasia, are multisystem disorders with cardiovascular, autonomic and peripheral nerve involvement. There are numerous investigational modalities available to diagnose systemic amyloidosis and to assess the extent of organ involvement, but it is frequently misdiagnosed due to its heterogeneous clinical presentations and misleading investigation findings. An accurate and timely diagnosis of amyloid neuropathy can greatly impact on the outcomes for patients, especially as there will soon be new gene-silencing treatments for hereditary transthyretin amyloidosis.

Prognostic utility of the Perugini grading of 99mTc-DPD scintigraphy in transthyretin (ATTR) amyloidosis and its relationship with skeletal muscle and soft tissue amyloid

Aims

High-grade (Perugini grade 2 or 3) cardiac uptake on bone scintigraphy with 99mTechnetium labelled 3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) has lately been confirmed to have high diagnostic sensitivity and specificity for cardiac transthyretin (ATTR) amyloidosis. We sought to determine whether patient stratification by Perugini grade on 99mTc-DPD scintigraphy has prognostic significance in ATTR amyloidosis.

Methods and results

Patient survival from time of 99mTc-DPD scintigraphy was determined in 602 patients with ATTR amyloidosis, including 377 with wild-type ATTR (ATTRwt) and 225 with mutant ATTR (ATTRm) amyloidosis. Patients were stratified according to Perugini grade (0-3) on 99mTc-DPD scan. The prognostic significance of additional patient and disease-related factors at baseline were determined. In the whole cohort, the finding of a Perugini grade 0 99mTc-DPD scan (n = 28) was invariably associated with absence of cardiac amyloid according to consensus criteria as well as significantly better patient survival compared to a Perugini grade 1 (n = 28), 2 (n = 436) or 3 (n = 110) 99mTc-DPD scan (P < 0.005). There were no differences in survival between patients with a grade 1, grade 2 or grade 3 99mTc-DPD scan in ATTRwt (n = 369), V122I-associated ATTRm (n = 92) or T60A-associated ATTRm (n = 59) amyloidosis. Cardiac amyloid burden, determined by equilibrium contrast cardiac magnetic resonance imaging, was similar between patients with Perugini grade 2 and Perugini grade 3 99mTc-DPD scans but skeletal muscle/soft tissue to femur ratio was substantially higher in the latter group (P < 0.001).

Conclusion

99mTc-DPD scintigraphy is exquisitely sensitive for identification of cardiac ATTR amyloid, but stratification by Perugini grade of positivity at diagnosis has no prognostic significance.

Genotype and Phenotype of Transthyretin Cardiac Amyloidosis: THAOS (Transthyretin Amyloid Outcome Survey)

BACKGROUND

Transthyretin amyloidosis (ATTR) is a heterogeneous disorder with multiorgan involvement and a genetic or nongenetic basis.

OBJECTIVES

The goal of this study was to describe ATTR in the United States by using data from the THAOS (Transthyretin Amyloidosis Outcomes Survey) registry.

METHODS

Demographic, clinical, and genetic features of patients enrolled in the THAOS registry in the United States (n = 390) were compared with data from patients from other regions of the world (ROW) (n = 2,140). The focus was on the phenotypic expression and survival in the majority of U.S. subjects with valine-to-isoleucine substitution at position 122 (Val122Ile) (n = 91) and wild-type ATTR (n = 189).

RESULTS

U.S. subjects are older (70 vs. 46 years), more often male (85.4% vs. 50.6%), and more often of African descent (25.4% vs. 0.5%) than the ROW. A significantly higher percentage of U.S. patients with ATTR amyloid seen at cardiology sites had wild-type disease than the ROW (50.5% vs. 26.2%). In the United States, 34 different mutations (n = 201) have been reported, with the most common being Val122Ile (n = 91; 45.3%) and Thr60Ala (n = 41; 20.4%). Overall, 91 (85%) of 107 patients with Val122Ile were from the United States, where Val122Ile subjects were younger and more often female and black than patients with wild-type disease, and had similar cardiac phenotype but a greater burden of neurologic symptoms (pain, numbness, tingling, and walking disability) and worse quality of life. Advancing age and lower mean arterial pressure, but not the presence of a transthyretin mutation, were independently associated with higher mortality from a multivariate analysis of survival.

CONCLUSIONS

In the THAOS registry, ATTR in the United States is overwhelmingly a disorder of older adult male subjects with a cardiac-predominant phenotype. Val122Ile is the most common transthyretin mutation, and neurologic phenotypic expression differs between wild-type disease and Val122Ile, but survival from enrollment in THAOS does not. (Transthyretin-Associated Amyloidoses Outcome Survey [THAOS]; NCT00628745).

Secondary myopathy due to systemic diseases

Background

Some systemic diseases also affect the skeletal muscle to various degrees and with different manifestations. This review aimed at summarizing and discussing recent advances concerning the management of muscle disease in systemic diseases.

Method

Literature review by search of MEDLINE, and Current Contents with appropriate search terms.

Results

Secondary muscle disease occurs in infectious disease, endocrine disorders, metabolic disorders, immunological disease, vascular diseases, hematological disorders, and malignancies. Muscle manifestations in these categories include pathogen‐caused myositis, muscle infarction, rhabdomyolysis, myasthenia, immune‐mediated myositis, necrotising myopathy, or vasculitis‐associated myopathy. Muscle affection may concern only a single muscle, a group of muscles, or the entire musculature. Severity of muscle affection may be transient or permanent, may be a minor part of or may dominate the clinical picture, or may be mild or severe, requiring invasive measures including artificial ventilation if the respiratory muscles are additionally involved. Diagnostic work‐up is similar to that of primary myopathies by application of non‐invasive and invasive techniques. Treatment of muscle involvement in systemic diseases is based on elimination of the underlying cause and supportive measures. The prognosis is usually fair if the causative disorder is effectively treatable but can be fatal in single cases if the entire musculature including the respiratory muscles is involved, in case of infection, or in case of severe rhabdomyolysis.

Conclusion

Secondary muscle manifestations of systemic diseases must be addressed and appropriately managed. Prognosis of secondary muscle disease in systemic diseases is usually fair if the underlying condition is accessible to treatment.

A study of the neuropathy associated with transthyretin amyloidosis (ATTR) in the UK

BACKGROUND

Hereditary transthyretin amyloidosis (ATTR) is usually characterised by a progressive peripheral and autonomic neuropathy often with associated cardiac failure and is due to dominantly inherited transthyretin mutations causing accelerated amyloid deposition. The UK population is unique in that the majority of patients have the T60A missense mutation in ATTR where tyrosine is replaced by adenine at position 60. This has been traced to a single founder mutation from north-west Ireland. The neuropathy phenotype is less well described than the cardiac manifestations in this group.

METHODS

We present the findings from an observational cohort study of patients with ATTR attending the National Hospital Inherited Neuropathy Clinic between 2009 and 2013. Detailed clinical neurological and electrophysiological data were collected on all patients alongside correlating autonomic and cardiac assessments. Follow-up data were available on a subset.

RESULTS

Forty-four patients with genetically confirmed ATTR were assessed; 37 were symptomatic; mean age at onset=62 years, range=38-75 years; 75.7% male. T60A was the most common mutation (17/37), followed by V30M (5/37). A severe, rapidly progressive, predominantly length dependent axonal sensorimotor neuropathy was the predominant phenotype. T60A patients were distinguished by earlier and more frequent association with carpal tunnel syndrome; a predominance of negative sensory symptoms at onset; significant vibration deficits; and a non-length dependent progression of motor deficit. Progression of the neuropathy was observed over a relatively short follow-up period (2 years) in 20 patients with evidence of clinically measurable annual change in Medical Research Council (MRC) sum score (-1.5 points per year) and Charcot Marie Tooth Neuropathy Score (CMTNS:2.7 points per year), and a congruent trend in the electrophysiological measures used.

CONCLUSION

The description of the ATTR neuropathy phenotype, especially in the T60A patients, should aid early diagnosis as well as contribute to the understanding of its natural history.

Heart Disease in Disorders of Muscle, Neuromuscular Transmission, and the Nerves

Little is known regarding cardiac involvement (CI) by neuromuscular disorders (NMDs). The purpose of this review is to summarise and discuss the major findings concerning the types, frequency, and severity of cardiac disorders in NMDs as well as their diagnosis, treatment, and overall outcome. CI in NMDs is characterized by pathologic involvement of the myocardium or cardiac conduction system. Less commonly, additional critical anatomic structures, such as the valves, coronary arteries, endocardium, pericardium, and even the aortic root may be involved. Involvement of the myocardium manifests most frequently as hypertrophic or dilated cardiomyopathy and less frequently as restrictive cardiomyopathy, non-compaction, arrhythmogenic right-ventricular dysplasia, or Takotsubo-syndrome. Cardiac conduction defects and supraventricular and ventricular arrhythmias are common cardiac manifestations of NMDs. Arrhythmias may evolve into life-threatening ventricular tachycardias, asystole, or even sudden cardiac death. CI is common and carries great prognostic significance on the outcome of dystrophinopathies, laminopathies, desminopathies, nemaline myopathy, myotonias, metabolic myopathies, Danon disease, and Barth-syndrome. The diagnosis and treatment of CI in NMDs follows established guidelines for the management of cardiac disease, but cardiotoxic medications should be avoided. CI in NMDs is relatively common and requires complete work-up following the establishment of a neurological diagnosis. Appropriate cardiac treatment significantly improves the overall long-term outcome of NMDs.