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Hung up reflex -Clinical significance

Knee jerk is a deep tendon reflex mediated by L4 segment of spinalcord
Usually in  deep tendon reflex  when  a stimulus is given there is a reflex action takes place, but in hypothyroidism the limb returns slowly to its neutral position.That is there is slowness of the relaxation phase of deep tendon reflexes
In hypothyroidism both the contraction and the relaxation phases of the tendon reflex may be prolonged, which results  in 'hung-up' reflexes.
Clinical significance
Hung-up reflex may be seen in
  • Hypothyroidism.
  • The 'hung-up' knee jerk is a specific, but rarely appreciated sign in  Huntington's Disease