Journal of the Louisiana State Medical Society
patterns of weakness that inevitably lead to respiratory failure and death. Myasthenia gravis is an autoimmune disorder of neuromuscular signal transmission, resulting in fatigable weakness that commonly involves the ocular muscles and can also involve the respiratory muscles. Inflammatory myopathies arise from immune-mediated muscle injury and can progress from proximal muscle weakness to respiratory involvement. Differentiating these neuromuscular conditions requires a high clinical suspicion, recognition of the pattern of weakness, and laboratory stud- ies including electromyography and/or muscle biopsies. Sporadic IBM is a devastating rheumatologic disease in the class of inflammatory myopathies. Prevalence varies from 1 to 15 per million people and appears to be linked to the HLA-DR3 autoimmune allele cluster. 1 IBM is more com- mon among the elderly population, rarely occurring in those below age 50, and tends to afflict men more than women. 2 Unlike polymyositis and dermatomyositis, IBM tends to be associated with insidious onset of muscle weakness, most notably involving the quadriceps, finger flexors, and ankle dorsiflexors. 3 Whilemost cases of IBM includeweakness that is usually symmetric and in the proximal muscles, there is an important subgroup of patients that have predominantly asymmetric or distal involvement at various locations, and this proportion is greater than in polymyositis. Dysphagia is also common. While respiratorymuscle weakness leading to respiratory failure is a common cause of death among those with IBM, it is considered extremely rare and unusual as a presenting symptom of the disease. 4 While a good clinical history is essential in detecting IBM, electrodiagnostic and pathologic confirmation is neces- sary. Unlike polymyositis, laboratory studies are generally unremarkable in IBM, with muscle enzymes generally nor- mal or onlymildly elevated. 5 Electromyography is revealing of a neurogenic and myopathic pattern, but it is generally nonspecific among the inflammatorymyopathies. 6 Themost definitive diagnostic test is a biopsy of an affected muscle. Pathologically unique to IBM are the presence of intramus- cular vacuoles and amyloid deposits. 7 The pathophysiol- ogy of IBM is believed to be related to the accumulation of injurious molecules and proteins in the muscle fibers. 8 Cells thought to be associated with muscle fiber injury include T-cells, dendritic-cells, and plasma-cells that infiltrate the fascicular myofibers. 9 One possible antigen involved in the immune response leading to muscle fiber damage is alphaB crystallin. 10 Furthermore, deposition of proteins such as beta-amyloid and phosphorylated microtubule-associated protein tau (MAPT) may contribute to muscle injury. 11,12 IBM is unique among the inflammatory myopathies because of its relative resistance to standard immuno- therapy (prednisone, methotrexate, and azathioprine), with continued gradual deterioration of muscle strength. Physical and occupational therapy may play a role in pa- tient rehabilitation and palliation. The most common cause of death among patients with IBM is respiratory infection, while direct respiratory failure from muscle weakness is also possible but rarer.
We present a case of IBM presenting primarily with symptoms of dyspnea in an individual with impaired cardiopulmonary reserve due to his underlying cardio- pulmonary comorbidities. In retrospect, even though the patient’s major complaint was dyspnea, his foot drop and gait impairment were subtle clues to an underlying neu- romuscular disorder. The restrictive respiratory pattern demonstrated on his pulmonary function tests also hinted at a neuromuscular abnormality. While intrinsic lung diseases such as interstitial lung disease may cause these findings on pulmonary function testing, extrinsic factors such as obesity and neuromuscular disorders can also contribute to a restric- tive pulmonary pattern. The patient expired approximately two weeks after his diagnosis of inclusion body myositis. This case highlights the importance of early diagnosis of IBM, whichwould allow for the patient and family to discuss treatment options and plan for end-of-life care. CONCLUSIONS Our patient’s presenting symptom was progressive dyspnea that failed to respond to aggressive management of multiple cardiac comorbidities. The diagnosis of IBM was eventuallymade as respiratory failure progressed. IBM uncommonly presents as respiratory failure fromdiaphrag- matic weakness. A high suspicion from a detailed history and physical exam was required to make the correct diag- nosis in our patient after the more common cardiovascular and pulmonary causes of dyspnea were ruled out. ACKNOWLEDGEMENTS We would like to acknowledge Dr. Andrew Engel, Professor of Neurology at the Mayo Clinic in Rochester, for his contribution of the muscle biopsy pathology images. REFERENCES 1. Mastaglia FL. Sporadic inclusion body myositis: variability in prevalence and phenotype and influence of the MHC. Acta Myol 2009;28:66-71. 2. Wilson FC, Ytterberg SR, St Sauver JL, Reed AM. Epidemiology of sporadic inclusion body myositis and polymyositis in Olmsted County, Minnesota. J Rheumatol 2008;35:445-7. 3. Greenberg SA. Inclusion body myositis. Curr Opin Rheumatol 2011;23:574-8. 4. Voermans NC, Vaneker M, Hengstman GJ, et al. Primary respiratory failure in inclusion body myositis. Neurology 2004;63:2191-2. 5. Lotz BP, Engel AG, Nishino H, Stevens JC, Litchy WJ. Inclusion body myositis. Observations in 40 patients. Brain 1989;112 (Pt 3):727-47. 6. Solorzano GE, Phillips LH, 2nd. Inclusion body myositis: diagnosis, pathogenesis, and treatment options. Rheum Dis Clin North Am 2011;37:173-83, v. 7. Engel WK, Askanas V. Inclusion-body myositis: clinical, diagnostic, and pathologic aspects. Neurology 2006;66:S20-9. 8. Dalakas MC. Pathophysiology of inflammatory and autoimmune myopathies. Presse Med 2011;40:e237-47.
256 J La State Med Soc VOL 166 November/December 2014
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