Myopathy

In medicine, myopathy is a disease of the muscle[1] in which the muscle fibers do not function properly. This results in muscular weakness. Myopathy means muscle disease (Greek : myo- muscle + patheia -pathy : suffering). This meaning implies that the primary defect is within the muscle, as opposed to the nerves ("neuropathies" or "neurogenic" disorders) or elsewhere (e.g., the brain). Muscle cramps, stiffness, and spasm can also be associated with myopathy.

Myopathy
SpecialtyRheumatology, Neuromuscular medicine

Capture myopathy can occur in wild or captive animals, such as deer and kangaroos, and leads to morbidity and mortality.[2] It usually occurs as a result of stress and physical exertion during capture and restraint.

Muscular disease can be classified as neuromuscular or musculoskeletal in nature. Some conditions, such as myositis, can be considered both neuromuscular and musculoskeletal.

Signs and symptoms

Common symptoms include muscle weakness, cramps, stiffness, and tetany.

Systemic diseases

Myopathies in systemic disease results from several different disease processes including endocrine, inflammatory, paraneoplastic, infectious, drug- and toxin-induced, critical illness myopathy, metabolic, collagen related,[3] and myopathies with other systemic disorders. Patients with systemic myopathies often present acutely or sub acutely. On the other hand, familial myopathies or dystrophies generally present in a chronic fashion with exceptions of metabolic myopathies where symptoms on occasion can be precipitated acutely. Metabolic myopathies, which affect the production of ATP within the muscle cell, typically present with dynamic (exercise-induced) rather than static symptoms.[4] Most of the inflammatory myopathies can have a chance association with malignant lesion; the incidence appears to be specifically increased only in patients with dermatomyositis.[5]

There are many types of myopathy. ICD-10 codes are provided here where available.

Inherited forms

Acquired
  • (G72.0 - G72.2) External substance induced myopathy
  • (M33.0-M33.1)
    • Dermatomyositis produces muscle weakness and skin changes. The skin rash is reddish and most commonly occurs on the face, especially around the eyes, and over the knuckles and elbows. Ragged nail folds with visible capillaries can be present. It can often be treated by drugs like corticosteroids or immunosuppressants. (M33.2)
    • Polymyositis produces muscle weakness. It can often be treated by drugs like corticosteroids or immunosuppressants.
    • Inclusion body myositis is a slowly progressive disease that produces weakness of hand grip and straightening of the knees. No effective treatment is known.
  • (M60.9) Benign acute childhood myositis
  • (M61) Myositis ossificans
  • (M62.89) Rhabdomyolysis and (R82.1) myoglobinurias

The Food and Drug Administration is recommending that physicians restrict prescribing high-dose Simvastatin (Zocor, Merck) to patients, given an increased risk of muscle damage. The FDA drug safety communication stated that physicians should limit using the 80-mg dose unless the patient has already been taking the drug for 12 months and there is no evidence of myopathy. "Simvastatin 80 mg should not be started in new patients, including patients already taking lower doses of the drug," the agency states.

Myocardium / cardio-myopathy

[9]

Differential diagnosis

At birth

  • None as systemic causes; mainly hereditary

Onset in childhood

  • Inflammatory myopathies – dermatomyositis, polymyositis (rarely)
  • Infectious myopathies
  • Endocrine and metabolic disorders – hypokalemia, hypocalcemia, hypercalcemia

Onset in adulthood[5]

  • Inflammatory myopathies – polymyositis, dermatomyositis, inclusion body myositis, viral (HIV)
  • Infectious myopathies
  • Endocrine myopathies – thyroid, parathyroid, adrenal, pituitary disorders
  • Toxic myopathies – alcohol, corticosteroids, narcotics, colchicines, chloroquine
  • Critical illness myopathy
  • Metabolic myopathies
  • Paraneoplastic myopathy

Treatments

Because different types of myopathies are caused by many different pathways, there is no single treatment for myopathy. Treatments range from treatment of the symptoms to very specific cause-targeting treatments. Drug therapy, physical therapy, bracing for support, surgery, and massage are all current treatments for a variety of myopathies.

References
  1. "Myopathy - Definition from the Merriam-Webster Online Dictionary".
  2. Green-Barber JM, Stannard HJ, Old JM (2018). "A suspected case of myopathy in a free-ranging eastern grey kangaroo (Macropus giganteus)". Australian Mammalogy. 40: 122–126. doi:10.1071/AM16054.
  3. Voermans NC, van Alfen N, Pillen S, Lammens M, Schalkwijk J, Zwarts MJ, van Rooij IA, Hamel BC, van Engelen BG (June 2009). "Neuromuscular involvement in various types of Ehlers-Danlos syndrome". Ann. Neurol. 65 (6): 687–97. doi:10.1002/ana.21643. PMID 19557868. S2CID 22600065.
  4. Darras, Basil T.; Friedman, Neil R. (February 2000). "Metabolic myopathies: a clinical approach; part I". Pediatric Neurology. 22 (2): 87–97. doi:10.1016/S0887-8994(99)00133-2. PMID 10738913.
  5. Chawla J (2011). "Stepwise approach to myopathy in systemic disease". Front Neurol. 2: 49. doi:10.3389/fneur.2011.00049. PMC 3153853. PMID 21886637.
  6. Seene T (July 1994). "Turnover of skeletal muscle contractile proteins in glucocorticoid myopathy". J. Steroid Biochem. Mol. Biol. 50 (1–2): 1–4. doi:10.1016/0960-0760(94)90165-1. PMID 8049126. S2CID 27814895.
  7. "Information On Sycamore Poisoning". Rainbow Equine Hospital. Retrieved 16 May 2017.
  8. "Equine Atypical Myopathy toxin and biochemical tests and tree sample testing available at the RVC". Royal Veterinary college - University of London. 13 February 2017. Retrieved 16 May 2017.
  9. "2019 ICD-10-CM Diagnosis Code I42.9: Cardiomyopathy, unspecified". The Web's Free 2019 ICD-10-CM/PCS Medical Coding Reference. 1 October 2018. Retrieved 5 February 2019.
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