Spasticity and Rigidity

Q: What is the difference between spasticity and rigidity?

  

Answer: Simple clinical exam at the bedside provides various clues to the underlying pathology. During neuro exam, it may be of importance to differentiate between spasticity and rigidity.

Spasticity is also known as "clasp-knife phenomenon". Here a limb moves freely for a little while, then there is a "catch" requiring a force to move the limb, followed by a sudden release, and limb move freely again. 

Rigidity requires increased resistance throughout the movement and get accentuated by distracting the patient. There are two kinds of rigidity. When resistance is uniform throughout the movement, is called Lead-pipe rigidity. In contrast, resistance which has rhythmic interruption is called Cogwheel rigidity.

It would be of interest to know the difference between these two phenomena is intriguing academicians for the last six decades (see reference # 2).

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References:

1. Fearon C, Doherty L, Lynch T. How Do I Examine Rigidity and Spasticity?. Mov Disord Clin Pract. 2015;2(2):204. Published 2015 Mar 28. doi:10.1002/mdc3.12147

2. HERMAN R. The physiologic basis of tone, spasticity and rigidity. Arch Phys Med Rehabil. 1962 Mar;43:108-14. PMID: 13906696.