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inclusion body myositis (inflammatory myositis, IBM)

Etiology: 1) unknown 2) not associated with connective tissue disease* 3) not associated with malignancy* * distinguishing features from polymyositis/dermatomyositis Epidemiology: 1) occurs in older patients (> 50 years)* - mean age of onset 61 years [3] 2) occurs more frequently in males than females* 3) most common form of myositis in patients presenting > 60 years of age [2] * distinguishing features from polymyositis/dermatomyositis Pathology: 1) eosinophilic inclusions & rimmed vacuoles with basophilic enhancement (amyloid)*# 2) cricopharyngeal involvement (50%), thus dysphagia [2] 2) otherwise resembles polymyositis/dermatomyositis * distinguishing feature from polymyositis/dermatomyositis # amyloid is cross-reactive with amyloid-beta peptide antibodies Genetics: - familial association Clinical manifestations: 1) insidious onset, occurring over many years 2) both distal & proximal flexor muscle weakness* - distal muscle weakness may not be apparent in lower extremities [8] 3) weakness generally symmetric, but may be asymmetric* 4) flexor atrophy of the forearms occurs early 5) quadriceps, wrist & finger flexors frequently involved 6) swallowing may be affected (dysphagia) in 50% [2,8] 7) muscle pain is unusual 8) patellar reflex may be decreased [3] 9) extramuscular manifestations are rare [2] 10) generally no rash [2] 11) waddling gait [2] * distinguishing features from polymyositis/dermatomyositis Laboratory: 1) serum creatine kinase: a) minimal to several fold increase* (10-12 fold increase) b) typically < 1200 U/L [2] 2) absence of autoantibodies [2] - except anti-cytoplasmic 5' nucleotidase 1A (anti-NT5c1A Ab) in 50% 3) always check serum TSH when evaluating myopathy * distinguishing feature from polymyositis/dermatomyositis Special laboratory: 1) electromyography (non-specific) a) myopathy b) neuropathy* 2) muscle biopsy - can help confirm diagnosis - not necessary when clinical features are characteristic [2] * distinguishing feature from polymyositis/dermatomyositis Radiology: - magnetic resonance imaging of muscle can identify sites for muscle biopsy, aid in the diagnosis & help assess response to treatment [2] Differential diagnosis: 1) pharmaceutical agents 2) toxins 3) endocrine disorder 4) electrolyte imbalance 5) infection 6) paraneoplastic syndrome 7) neuromuscular disorder [3] Complications: - risk of aspiration from cricopharyngeal muscle involvement, resulting in dysphagia - not associated with increase risk of malignancy [8] Management: 1) responds poorly to prednisone & immunosuppressive agents 2) rate of deterioration in some patients may be slowed by glucocorticoids or intravenous immune globulin [2] - unlikely to respond to intravenous immune globulin if not responsive to glucocorticoids [2] 3) course of disease is slow, progressive weakness - progression to wheel chair dependence in 10-15 years [2] 4) exercise may be of benefit, but supporting data is limited [8] 5) physical therapy [2]

Related

dermatomyositis inclusion body myopathy polymyositis

General

myositis (inflammatory myopathy)

Database Correlations

OMIM 147421

References

  1. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 877
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 1998, 2006, 2009, 2012, 2015, 2018, 2022. - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  3. Weiner S, In: UCLA Intensive Course in Geriatric Medicine & Board Review, Marina Del Ray, CA, Sept 12-15, 2001
  4. LaFeria F, UCLA Brain Matters, Sept 30, 2002
  5. Needham M, Mastaglia FL. Inclusion body myositis: current pathogenetic concepts and diagnostic and therapeutic approaches. Lancet Neurol. 2007 Jul;6(7):620-31. PMID: 17582362
  6. Chahin N, Engel AG. Correlation of muscle biopsy, clinical course, and outcome in PM and sporadic IBM. Neurology. 2008 Feb 5;70(6):418-24. Epub 2007 Sep 19. PMID: 17881720
  7. Amato AA, Barohn RJ. Inclusion body myositis: old and new concepts. J Neurol Neurosurg Psychiatry. 2009 Nov;80(11):1186-93 PMID: 19864656
  8. Geriatric Review Syllabus, 8th edition (GRS8) Durso SC and Sullivan GN (eds) American Geriatrics Society, 2013
  9. Amato AA, Barohn RJ. Inclusion body myositis: old and new concepts. J Neurol Neurosurg Psychiatry. 2009 Nov;80(11):1186-93. Review. PMID: 19864656
  10. Johnson LG, Collier KE, Edwards DJ et al Improvement in aerobic capacity after an exercise program in sporadic inclusion body myositis. J Clin Neuromuscul Dis. 2009 Jun;10(4):178-84. PMID: 19494728
  11. Engel WK, Askanas V Inclusion-body myositis: clinical, diagnostic, and pathologic aspects. Neurology. 2006 Jan 24;66(2 Suppl 1):S20-9. PMID: 16432141
  12. Needham M, Mastaglia FL. Sporadic inclusion body myositis: A review of recent clinical advances and current approaches to diagnosis and treatment. Clin Neurophysiol. 2016 Mar;127(3):1764-73. PMID: 26778717
  13. NINDS Inclusion Body Myositis Information Page https://www.ninds.nih.gov/Disorders/All-Disorders/Inclusion-Body-Myositis-Information-Page