Hung-up Knee Jerk Reflex

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  • Hung-up knee jerk is a common presentation in Huntington’s disease.
  • It causes the legs to be extended for several seconds on stimulation of the patellar tendon.
  • Deep tendon reflexes are also often seen in patients with hypothyroidism.

A 54-year-old woman presented to the neurology clinic with gait that had worsened over the course of 2 years. She had a history of papillary thyroid cancer for which she underwent thyroidectomy. She also developed hypothyroidism after the thyroidectomy.

The patient was currently on levothyroxine therapy and euthyroid. Physical examination showed generalised deep-tendon hyperreflexia, irritability, disinhibition, mild dementia, protrusion, motor impersistence of the tongue and generalised chorea. The patient’s legs were notably extended for several seconds after the patellar tendon was stimulated. The findings were consistent with the diagnosis of hung-up knee jerk.

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For further evaluation, a magnetic resonance imaging of the head was performed, which showed atrophy of the caudate nuclei. Whereas, genetic testing showed expanded CAG repeats in HTT. The findings were consistent with Huntington’s disease.

Hung-up knee jerk

The hung-up knee jerk is commonly observed in patients Huntington’s disease and benign hereditary or Sydenham’s chorea. The hung-up knee jerk reflex should be distinguished from delayed relaxation of deep-tendon reflexes which is often seen in patients with hypothyroidism. The reflex is a rarely appreciated clinical sign of Huntington’s disease.

The patient was treated with haloperidol after which the hung-up knee jerk resolved.

References

Fukumoto, T., & Miyamoto, R. (2020). Hung-up Knee Jerk in Huntington’s Disease. New England Journal of Medicine382(7), e10.

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Dr. Aiman Shahab is a dentist with a bachelor’s degree from Dow University of Health Sciences. She is an experienced freelance writer with a demonstrated history of working in the health industry. Skilled in general dentistry, she is currently working as an associate dentist at a private dental clinic in Karachi, freelance content writer and as a part time science instructor with Little Medical School. She has also been an ambassador for PDC in the past from the year 2016 – 2018, and her responsibilities included acting as a representative and volunteer for PDC with an intention to make the dental community of Pakistan more connected and to work for benefiting the underprivileged. When she’s not working, you’ll either find her reading or aimlessly walking around for the sake of exploring. Her future plans include getting a master’s degree in maxillofacial and oral surgery, settled in a metropolitan city of North America.

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