Introduction: Although peripheral neuropathy and cardiomyopathy are wellrecognized manifestations of transthyretin (ATTR) amyloidosis, myopathy has been rarely reported.
Methods:In this study we reviewed our muscle biopsy database (January 1998 to June 2018) to identify patients with ATTR amyloid myopathy confirmed by molecular or proteomic analysis. Clinical and laboratory findings were reviewed.
Results: We identified eight ATTR amyloid myopathy patients (5 hereditary ATTR [ATTRv] and 3 wild-type ATTR [ATTRwt]). Myopathy was the initial manifestation in all ATTRwt patients and followed peripheral neuropathy (4 patients) or cardiomyopathy (1 patient) in ATTRv patients. One ATTRv patient developed myopathy after liver transplant. Peripheral neuropathy and cardiac amyloidosis occurred in seven and six patients, respectively. Muscle biopsy showed interstitial amyloid deposition in all patients, rare necrotic/regenerating fibers in six, and vacuoles in four. Discussion: Myopathy can be the initial manifestation of ATTRwt amyloidosis and can precede the peripheral neuropathy or occur after liver transplant in ATTRv amyloidosis. K E Y W O R D S amyloid myopathy, ATTR amyloid myopathy, ATTR amyloidosis, myopathy, neuromyopathy, transthyretin amyloidosis Abbreviations: ATTR, transthyretin; ATTRv, hereditary or mutated transthyretin; ATTRwt, wild-type transthyretin; CIDP, chronic inflammatory demyelinating polyradiculoneuropathy;CK, creatine kinase; EMG, electromyography; MS-P, mass spectrometry-based proteomics; MUP, motor unit action potential; TTR, transthyretin gene.
Recently, guidelines have been outlined for management of immune-related adverse events occurring with immune checkpoint inhibitors in cancer, irrespective of affected organ systems. Increasingly, these complications have been recognized as including diverse neuromuscular presentations, such as demyelinating and axonal length–dependent peripheral neuropathies, vasculitic neuropathy, myasthenia gravis, and myopathy. We present 2 cases of brachial plexopathy developing on anti–programmed cell death-1 checkpoint inhibitor therapies (pembrolizumab, nivolumab). Both cases had stereotypic lower-trunk brachial plexus–predominant onsets, and other clinical features distinguishing them from Parsonage-Turner syndrome (ie, idiopathic plexitis). Each case responded to withholding of anti–programmed cell death-1 therapy, along with initiation of high-dose methylprednisiolone therapy. However, both patients worsened when being weaned from corticosteroids. Discussed are the complexities in the decision to add a second-line immunosuppressant drug, such as infliximab, when dealing with neuritis attacks, for which improvement may be prolonged, given the inherent slow recovery seen with axonal injury. Integrated care with oncology and neurology is emphasized as best practice for affected patients.
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