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Related Concept Videos

Alterations in Muscle Tone lll01:11

Alterations in Muscle Tone lll

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Rigidity and myotonia are distinct abnormalities of muscle tone that affect resistance and relaxation during movement. Although both involve altered muscle contraction, they arise from different neurological and muscular mechanisms.CharacteristicsRigidity is characterized by uniform resistance to passive movement across the entire range, independent of speed, affecting flexors and extensors equally. It may appear as lead-pipe rigidity (smooth, constant resistance) or cogwheel rigidity...
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Disorders of the Skeletal Muscle01:28

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The clinical conditions affecting the skeletal muscle tissue are broadly categorized as musculoskeletal and neuromuscular disorders.
Musculoskeletal disorders
Musculoskeletal disorders involve injuries and conditions affecting the skeletal muscles and associated connective tissues. These disorders can arise from acute biomechanical stresses or chronic overuse and can occur across different age groups. Common injuries include sprains, fractures, and muscular strains, often resulting from...
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Alterations in Muscle Tone ll01:12

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Alterations in muscle tone are common manifestations of neurological disorders and reflect dysfunction within different nervous system regions. Spasticity, paratonia, and dystonia represent distinct forms of hypertonia, each with unique mechanisms, clinical features, and diagnostic importance.CharacteristicsSpasticity happens from upper motor neuron lesions and is characterized by velocity-dependent resistance to passive movement. Clinical features include:Exaggerated deep tendon reflexesClonus...
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Myasthenia Gravis ll: Pathophysiology01:22

Myasthenia Gravis ll: Pathophysiology

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The disease process of myasthenia gravis begins at the neuromuscular junction, where antibodies attack key proteins needed for muscle activation. This immune reaction weakens signal transmission, leading to the characteristic muscle fatigue and weakness that define the condition.Immune-Mediated DamageIn most individuals, antibodies target acetylcholine receptors (AChRs) on the postsynaptic membrane of muscle cells. By blocking acetylcholine binding, these antibodies prevent the nerve signal...
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Myasthenia Gravis: Diagnostic Tests01:15

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Myasthenia gravis is an autoimmune condition affecting neuromuscular transmission, causing generalized weakness in skeletal muscles. Initial diagnoses rely on patients' signs, symptoms, and medical history. The challenge lies in distinguishing myasthenia from other muscular dystrophies. An important diagnostic feature is the significant improvement of symptoms after administering anticholinesterase inhibitors.
The edrophonium test is a diagnostic tool for myasthenia gravis. It involves...
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ATP Synthase: Mechanism01:48

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In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased...
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Myoclonus in mitochondrial disorders.

Michelangelo Mancuso1, Daniele Orsucci, Corrado Angelini

  • 1Neurological Clinic, University of Pisa, Pisa, Italy.

Movement Disorders : Official Journal of the Movement Disorder Society
|February 11, 2014
PubMed
Summary

Myoclonus, a rare sign in mitochondrial disease, affects 3.6% of patients. It is not solely linked to epilepsy in MERRF patients, often appearing with cerebellar ataxia instead.

Keywords:
8344A>GataxiamtDNAmyoclonic epilepsymyoclonus

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Area of Science:

  • Neurology
  • Genetics
  • Mitochondrial Diseases

Background:

  • Myoclonus is a key feature for diagnosing MERRF (myoclonic epilepsy with ragged red fibers).
  • The prevalence of myoclonus in mitochondrial diseases is not well-established.
  • Mitochondrial disorders encompass a range of genetic conditions affecting cellular energy production.

Purpose of the Study:

  • To determine the prevalence of myoclonus in a large cohort of mitochondrial disease patients.
  • To clinically characterize mitochondrial patients presenting with myoclonus.
  • To investigate the relationship between myoclonus, specific genotypes, and phenotypes in mitochondrial disorders.

Main Methods:

  • Analysis of clinical and molecular data from the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases" database.
  • Review of records for patients with myoclonus as a clinical feature.
  • Correlation of myoclonus presence with specific mutations (e.g., 8344A>G) and clinical presentations (epilepsy, ataxia).

Main Results:

  • Myoclonus is an uncommon feature, found in 3.6% of 1,086 mitochondrial disease patients.
  • Myoclonus is not strictly associated with a specific genotype or phenotype.
  • Only one-third of MERRF patients carry the common 8344A>G mutation.
  • Myoclonus in MERRF patients is more frequently associated with cerebellar ataxia than epilepsy.
  • The term "myoclonic epilepsy" may be misleading for MERRF.

Conclusions:

  • Investigate mitochondrial dysfunction in patients with myoclonus, even if it's not a common symptom.
  • Clinical, histological, and biochemical data can guide the search for mitochondrial or nuclear DNA mutations.
  • The association of myoclonus with cerebellar ataxia rather than epilepsy in MERRF challenges the traditional syndromic name.