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Related Concept Videos

Alterations in Muscle Tone lll01:11

Alterations in Muscle Tone lll

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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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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The clinical conditions affecting the skeletal muscle tissue are broadly categorized as musculoskeletal and neuromuscular disorders.
Musculoskeletal disorders
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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.
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Multiple sclerosis is a chronic autoimmune disease of the central nervous system (CNS) that affects the brain, spinal cord, and optic nerves. It is an inflammatory demyelinating disorder and a leading cause of neurological disability in young adults.EpidemiologyMS commonly begins between 20 and 40 years of age and is twice as common in women. Its exact cause remains unclear, but genetic susceptibility contributes, with higher risk in first-degree relatives and identical twins. A greater...
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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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Updated: Jul 16, 2026

Muscle Velocity Recovery Cycles to Examine Muscle Membrane Properties
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VRK1-Related Motor Neuropathy With Upper Motor Neuron Signs and Selective Muscle Involvement.

Manoella Guerra de Albuquerque Bueno1, Diogo Fernandes Dos Santos2, Alexander M Rossor3

  • 1Department of Neuroscience and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.

Journal of the Peripheral Nervous System : JPNS
|July 15, 2026
PubMed
Summary

Genetic variants in the VRK1 gene cause a distinct motor neuron disease presenting as hereditary motor neuropathy (HMN) with specific MRI findings. This highlights the need for VRK1 gene testing in unresolved HMN cases.

Keywords:
VRK1distal hereditary motor neuropathyjuvenile ALSmotor neuron diseasemuscle MRIupper motor neuron signs

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Area of Science:

  • Neurology
  • Genetics
  • Medical Imaging

Background:

  • Hereditary motor neuropathies (HMN) are a diverse group of disorders with significant genetic variability.
  • Approximately 50% of HMN cases remain genetically unresolved, posing diagnostic challenges.
  • VRK1 gene variants are associated with a spectrum of neurological disorders, including motor neuron diseases.

Purpose of the Study:

  • To characterize the clinical, electrophysiological, and muscle MRI features of VRK1-related motor neuron disease.
  • To investigate a cohort of nine patients from five unrelated families with suspected VRK1-related disorders.
  • To establish a recognizable phenotype for VRK1-associated motor neuron disease.

Main Methods:

  • Next-generation sequencing (NGS) and Sanger sequencing were used to identify VRK1 variants in five families.
  • Nine affected individuals underwent detailed clinical evaluations, nerve conduction studies (NCS), and electromyography (EMG).
  • Whole-body muscle MRI (wbMRI) and brain/spinal imaging were performed on all patients.

Main Results:

  • Biallelic VRK1 variants were identified in nine patients, with symptom onset typically in the first decade.
  • All patients exhibited progressive distal muscle weakness, with neurogenic EMG findings and normal sensory NCS.
  • wbMRI showed a consistent pattern of posterior muscle compartment fatty infiltration; brain and spinal imaging were normal.

Conclusions:

  • Biallelic VRK1 mutations define a specific motor neuron disease phenotype combining features of distal hereditary motor neuropathy (dHMN) and upper motor neuron involvement.
  • A distinctive posterior-predominant muscle MRI pattern is a key characteristic of VRK1-related disorders.
  • Targeted VRK1 genetic testing is crucial for diagnosing unresolved hereditary motor neuropathy cases presenting with this phenotype.