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The Human Phenotype Ontology (HPO) is downloaded weekly from The file downloaded is considered the "last stable build" available for the ontology. For more about the HPO, view their website at

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Accession:HP:0002486 term browser browse the term
Definition:An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation.
Comment:Patients often describe myotonia as stiffness that is worse at the onset of activity and that improves with repeated muscle contractions. Myotonia tends to worsen in cold weather. Myotonia can be elicited by voluntary muscle contraction of by muscle percussion (e.g., by tapping the thenar eminence). During physical examination, myotonia may be elicited by asking the patient to make a tight fist and then quickly open the hand. Myotonia is caused by an abnormality in the muscle membrane, i.e., of the ion channels that control the contraction of muscle fibers.
Synonyms:exact_synonym: Delayed relaxation of muscle fibers after contraction;   Delayed relaxation of muscle fibres after contraction
 alt_id: HP:0003632;   HP:0003754;   HP:0003792
 xref: MSH:D009222;   SNOMEDCT_US:3434004;   UMLS:C0027125

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  Human phenotype 0
    Phenotypic abnormality 0
      Abnormality of the musculoskeletal system 0
        Abnormality of the musculature 0
          Abnormal muscle physiology 0
            Myotonia 0
              Cold-sensitive myotonia 0
              EMG: myotonic runs 0
              Handgrip myotonia 0
              Myotonia of the face 0
              Myotonia of the jaw 0
              Myotonia of the lower limb 0
              Myotonia of the upper limb 0
              Myotonia with warm-up phenomenon 0
              Paradoxical myotonia 0
              Percussion myotonia + 0
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