inclusion body myositis (inflammatory myositis, IBM)
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Etiology
- unknown
- not associated with connective tissue disease*
- not associated with malignancy*
* distinguishing features from polymyositis/dermatomyositis
Epidemiology
- occurs in older patients (> 50 years)*
- occurs more frequently in males than females*
- most common form of myositis in patients presenting > 60 years of age[2]
* distinguishing features from polymyositis/dermatomyositis
Pathology
- eosinophilic inclusions & rimmed vacuoles with basophilic enhancement (amyloid)*#
- cricopharyngeal involvement (50%), thus dysphagia[2]
- otherwise resembles polymyositis/dermatomyositis
* distinguishing feature from polymyositis/dermatomyositis
# amyloid is cross-reactive with amyloid-beta peptide antibodies
Genetics
- familial association
Clinical manifestations
- insidious onset, occurring over many years
- both distal & proximal flexor muscle weakness*
- distal muscle weakness may not be apparent in lower extremities[8]
- weakness generally symmetric, but may be asymmetric*
- flexor atrophy of the forearms occurs early
- quadriceps, wrist & finger flexors frequently involved
- swallowing may be affected (dysphagia) in 50%[2][8]
- muscle pain is unusual
- patellar reflex may be decreased[3]
- extramuscular manifestations are rare[2]
- generally no rash[2]
- waddling gait[2]
* distinguishing features from polymyositis/dermatomyositis
Laboratory
- serum creatine kinase:
- minimal to several fold increase* (10-12 fold increase)
- typically < 1200 U/L[2]
- absence of autoantibodies[2]
- except anti-cytoplasmic 5' nucleotidase 1A (anti-NT5c1A Ab) in 50%
- always check serum TSH when evaluating myopathy
* distinguishing feature from polymyositis/dermatomyositis
Diagnostic procedures
- electromyography (non-specific)
- 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]
Complications
- risk of aspiration from cricopharyngeal muscle involvement, resulting in dysphagia
- not associated with increase risk of malignancy[8]
Differential diagnosis
- pharmaceutical agents
- toxins
- endocrine disorder
- electrolyte imbalance
- infection
- paraneoplastic syndrome
- neuromuscular disorder[3]
Management
- responds poorly to prednisone & immunosuppressive agents
- 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]
- course of disease is slow, progressive weakness
- progression to wheel chair dependence in 10-15 years[2]
- exercise may be of benefit, but supporting data is limited[8]
- physical therapy[2]
More general terms
Additional terms
References
- ↑ Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 877
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 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 - ↑ 3.0 3.1 3.2 3.3 Weiner S, In: UCLA Intensive Course in Geriatric Medicine & Board Review, Marina Del Ray, CA, Sept 12-15, 2001
- ↑ LaFeria F, UCLA Brain Matters, Sept 30, 2002
- ↑ Needham M, Mastaglia FL. Inclusion body myositis: current pathogenetic concepts and diagnostic and therapeutic approaches. Lancet Neurol. 2007 Jul;6(7):620-31. PMID: https://www.ncbi.nlm.nih.gov/pubmed/17582362
- ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/17881720
- ↑ Amato AA, Barohn RJ. Inclusion body myositis: old and new concepts. J Neurol Neurosurg Psychiatry. 2009 Nov;80(11):1186-93 PMID: https://www.ncbi.nlm.nih.gov/pubmed/19864656
- ↑ 8.0 8.1 8.2 8.3 8.4 Geriatric Review Syllabus, 8th edition (GRS8) Durso SC and Sullivan GN (eds) American Geriatrics Society, 2013
- ↑ Amato AA, Barohn RJ. Inclusion body myositis: old and new concepts. J Neurol Neurosurg Psychiatry. 2009 Nov;80(11):1186-93. Review. PMID: https://www.ncbi.nlm.nih.gov/pubmed/19864656
- ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/19494728
- ↑ Engel WK, Askanas V Inclusion-body myositis: clinical, diagnostic, and pathologic aspects. Neurology. 2006 Jan 24;66(2 Suppl 1):S20-9. PMID: https://www.ncbi.nlm.nih.gov/pubmed/16432141
- ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/26778717
- ↑ NINDS Inclusion Body Myositis Information Page https://www.ninds.nih.gov/Disorders/All-Disorders/Inclusion-Body-Myositis-Information-Page
Patient information
inclusion body myositis patient information