Ultrasound optimizes EMG muscle selection in a patient with inclusion body myositis: A case report

Neuromuscular ultrasound is increasingly used in physical medicine and rehabilitation as it is low cost, radiation free, providesreal-time image acquisition, and is easily accessible. Neuromuscular ultrasound used during electrodiagnosis can help reduce the number of muscles that must be evaluated,can identify the most appropriate muscle to perform a biopsy on, and can help determine the severity and etiology of a pathologic condition (neurogenic atrophy, dystrophy, and inflammatory muscular disease). Neuromuscular ultrasound also can assist in identifying the appropriate muscle for an electromyography (EMG) evaluation forsevere muscle atrophy, such as in the case we now present. We present the case of a 72-year-old woman referred for an electrophysiological study because of generalized muscle weakness developing over 14 years. The disorder started in the proximal muscles of the upper extremities and affected hygiene and selfcare activities. Thereafter and gradually, the weakness extended toward the distal muscles of the upper extremities and in a lesser degree toward the lower extremities. In the last 4 years, the woman fell frequently and required the use of a wheelchair for movements in the community. On the physical examination, we found generalized muscle weakness with marked atrophy of the upper extremities and partial preservation of strength for thumb opposition and finger abduction 3/5. The other muscles of the upper extremities had traces of movement. On the lower extremities, we found a strength of 3/5 in the plantarflexion and dorsiflexion muscles of the ankle, 2/5 in the knee extensors, and 1/5 in the hip extensors. We found no sensory alterations. The patient was unable to climb stairs but could still walk short distances on flat surfaces at a speed of 0.14 m/s. Because of the severe atrophy of the muscles of the extremities, we decided to perform neuromuscular ultrasound before EMG, with the purpose of selecting the muscles that should be evaluated. In the muscles of the upper extremities, we observed a generalized alteration of the echo structure with an increase in echogenicity (Heckmat III) and atrophy with fat replacement, except for the flexor carpi radialis, triceps, and thenar region muscles. The muscular echo structure of the lower extremities showed a homogeneous increase in the echogenicity of the tibialis anterior and to a lesser degree of the gastrocnemius and quadriceps femoris. We performed EMG using ultrasound guidance on the tibialis anterior and quadriceps muscles, finding low amplitude motor units of short duration, with an early recruitment. We did not observe fibrillation potentials, positive sharp waves, or complex repetitive discharges. Using ultrasound guidance, we performed an EMG of the flexor carpi radialis muscle, finding an increase in the proportion of polyphasic motor units and the presence of motor potentials of high amplitude and long duration with a reduced recruitment pattern. Based on the phenotype, the age of onset and electromyographic findings, we considered the diagnosis of an inclusion body myositis (IBM). IBM is the most common acquired myopathy in people older than 50 years of age. The diagnosis is based on the clinical phenotype (asymmetric weakness predominantly on finger flexors and knee extensors, creatine phosphokinase level below 15 times the normal superior limit, age of onset over 45 years) and the histopathologic chracteristics. The severe forms show loss of ambulation and dysphagia. Different specific patterns of abnormality in the diagnostic images such as magnetic resonance imaging, computed tomography, and recently sonography have been identified. The typical ultrasound findings in IBM are selective changes in the muscle echotexture of the deep flexors of the fingers with preservation of the flexor carpi ulnaris and disturbance of the anterior compartment muscles of the leg, rectus femoris and gastrocnemius. The ultrasound findings are highly sensitive and specific and allow the differentiation of IBM from other muscle diseases. However, with the progression of the disease, muscular atrophy is less selective and the diagnosis is more difficult. In these cases, the electromyographic abnormalities help to clarify the clinical picture. The typical electromyographic findings in IBM are those of a myopathic pattern, although it has been observed in some patients, such as in the case we present, “pseudo” neurogenic potentials. These could be secondary to reinnervation of denervated and remodeled muscle fibers, probably related with the progressive myodegenerative process. In very advanced cases of the disease, such as the one we presented, the use of neuromuscular Received: 26 September 2020 Revised: 19 November 2020 Accepted: 5 April 2021