Misdiagnosis of Inclusion Body Myositis: Two Case Reports and a Retrospective Chart Review

Amaiak Chilingaryan; Richard A. Rison; Said R. Beydoun

Disclosures

J Med Case Reports. 2015;9(169) 

In This Article

Case Presentations

The local institutional review board approved this study. The case presentation portions of this report were prepared according to recent standardized guidelines.[7–9]

Patient 1

A 58-year-old man of Indian ethnicity with type 2 diabetes mellitus was referred to our hospital for a second-opinion neuromuscular evaluation. Four years prior, he had noted leg weakness, particularly in his thighs. After initial evaluation and diagnostic studies, his neurologist had diagnosed him with deconditioning and prescribed vitamin B 12 injections. A subsequent electrodiagnostic study revealed denervation changes in his upper extremity muscles and thoracic paraspinal muscles, leading to a diagnosis of amyotrophic lateral sclerosis (ALS), which the patient carried for nearly 1 year. He was prescribed riluzole and advised to plan for end of life.

When referred to our institution, the patient described weakness while climbing and descending stairs without upper extremity complaints. During his physical examination, he was noted to have atrophy in the quadriceps muscles with moderate weakness. Electromyography (EMG) showed increased membrane instability and early recruitment with fractionation of the motor unit potentials, showing a brief, small, abundant, polyphasic motor unit potential pattern. His creatine kinase (CK) level was elevated at 647IU/L. A muscle biopsy showed myopathic features with rimmed vacuoles characteristic of s-IBM. The patient was informed of his correct diagnosis and counseled on his prognosis. Patient 1 is represented as patient 8 in Table 1.

Patient 2

A 54-year-old Hispanic man developed weakness in his grip, followed 1 year later by lower extremity weakness. His CK level was 2400IU/L, and a muscle biopsy indicated polymyositis (PM). His initial therapy included prednisone followed by other immunosuppressive medications, including azathioprine, methotrexate, and mycophenolate mofetil. Although the patient's CK level decreased to 450IU/L, his condition continued to progress. Nine years later, he was evaluated at our neuromuscular clinic. At that time, he was unable to get up from a seated position, locked his knees while ambulating to avoid falls, and had severe weakness in his left hand and moderate weakness in his right hand. During his physical examination, he was noted to have asymmetric atrophy in the forearm flexor and the quadriceps muscles, with severe asymmetric weakness of knee extension and slight weakness in ankle dorsiflexion and plantarflexion. EMG showed active denervation with significant brief, small, abundant, polyphasic motor unit potentials. A repeat muscle biopsy showed variation in muscle fiber size, endomysial fibrosis, chronic inflammatory cells with macrophages, and rimmed vacuoles with basophilic stippling, all characteristic of s-IBM. The patient was counseled on his correct s-IBM diagnosis, and immunosuppressive therapy was discontinued. Patient 2 is represented as patient 9 in Table 1.

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