Anti-HMGCR myopathy misdiagnosed as motor neuron disease and complicated with COVID-19 infection

Abstract

Dear Editor-in-Chief, Inflammatory myopathy (IIMs) are a large group of potentially treatable myopathies in children and adults; necrotizing autoimmune myopathy is a distinct clinicopathologic entity, accounting for up to 19% of all IIM, and it is clinically characterized by proximalmuscle weakness of acute or subacute onset and high creatine kinase levels (CK) [1]. Most patients with necrotizing autoimmune myopathy have antibodies against signal recognition particle (SRP) or against 3-hydroxy-3methylglutaryl-coenzyme A reductase (HMGCR) [2]. The severe acute respiratory syndrome-correlated new coronavirus (SARS-CoV-2) is spreading worldwide since the beginning of 2020. The major clinical manifestations of the SARS-Cov-2 infection are due to pulmonary complications, and although most have mild symptoms, such as fever, headache, cough, dyspnea, myalgia, and anosmia, some develop acute respiratory distress syndrome that can result in death. Several neuromuscular symptoms were identified as part of the COVID-19 spectrum, and myalgias are reported in up to a half of patients with SARS-CoV-2 infection; instead, CK elevations depend on the disease severity, ranging from mild to severe rhabdomyolysis. Even if electromyography, muscle imaging, and muscle histopathology are not available to date, coronavirus infections may cause an IIM; few cases [3, 4] have described myositis triggered by SARS-CoV-2, and to date little is known [5] about the role of SARS-CoV-2 infection to determine relapse in previously affected patients. Here we present a case of a patient who was firstly diagnosed with a “lower motor neuron disease”, in which further assessment revealed the presence of necrotizing autoimmune myopathy. After a few weeks on steroid treatment, symptoms worsened and only subsequently this was proved to be a relapse triggered by SARS-CoV-2 infection. The patient is a 64-year-old male who came to our attention for a rehabilitation program due to a recent diagnosis of “lower motor neuron disease”. His first symptoms started 6 months before admission to our Centre, and they were characterized by a progressive weakness in his lower limbs with difficulty climbing stairs and walking for long distances, along with difficulty raising his arms over his head. He did not complain of any cramps or myalgias. No sensory or autonomic symptoms were reported. Three months after the onset of symptoms, the patient was admitted to a Neurology Clinic where he underwent several assessments including an EMG test which showed a diffuse increased spontaneous activity at rest; during voluntary contraction, polyphasic motor unit action potentials (MUAPs), with normal amplitude, duration and pattern of recruitment, were registered. CK level was> 4000–5000 U/L in three serial blood draws. Brain and spinal MRIs were all unremarkable. He was discharged with a diagnosis of “atypical motor neuron disease with predominant involvement of lower motor neuron”. The patient was started on riluzole. When the patient was admitted to our Centre for a neurorehabilitation program, neurological examination revealed a normal muscle bulk and tone without any fasciculations. He was unable to raise his arms above his head, and he required to push himself out of a chair using both hands and with a widened base. Gait was pretty stable. On manual strength testing, a significant symmetric loss of strength in his proximal muscles in both upper (UL) and lower limbs (LL) was evident. Specifically, according to the Medical Research Council (MRC) Scale, deltoid was 2+, biceps and triceps brachii 4+, iliopsoas 2+, hamstrings 4−, quadriceps 4+ and gluteus maximus 2+ bilaterally. Sensory and cerebellar systems were within normal limits. Deep tendon reflexes * Andrea Barp [email protected]