Stiffness of muscles occurs as a feature of all pyramidal and extrapyramidal disorders (as spasticity and rigidity, respectively), but the term stiffness is usually reserved for disorders in which stiffness is the principal symptom due to continuous motor unit activity within muscles. There may be associated muscle pain (cramp). Stiffness may be primarily of muscular origin (myotonia) or of neural origin (myokymia, neuromyotonia). Accompanying signs may prove helpful in diagnosis, such as slow muscle relaxation (myotonia), percussion irritability of muscle (myoedema), and spontaneous and exertional muscle spasms. Hyperlordotic posture is typical of stiff man/stiff person syndrome. Stiffness must be differentiated from both rigidity and spasticity.

Recognized causes of stiffness include: Stiff man/stiff person syndrome
Stiff limb syndrome
Progressive encephalomyelitis with rigidity +/−myoclonus Neuromyotonia (Isaac’s syndrome; armadillo syndrome) Schwartz-Jampel syndrome (chondrodystrophic myotonia) Tetanus
Strychnine poisoning

The stiff man/stiff person syndrome is probably of autoimmune pathogenesis since it is strongly associated with insulin-dependent diabetes mellitus and the presence of antibodies to glutamic acid decarboxylase (anti-GAD antibodies), the enzyme in the synthetic pathway of GABA. Intravenous immunoglobulin therapy may be of symptomatic benefit.



Barker R, Revesz T, Thom M, Marsden CD, Brown P. Review of 23 patients affected by the stiff man syndrome: clinical subdivision into stiff trunk (man) syndrome, stiff limb syndrome, and progressive encephalomyelitis with rigidity. Journal of Neurology, Neurosurgeryand Psychiatry 1998; 65: 633-640
Scolding NJ. Stiff man syndrome. In: Scolding NJ (ed.). Immunological and inflammatory disorders of the central nervous sys-tem. Oxford: Butterworth Heinemann 1999: 139-146
Thompson PD. Stiff people. In: Marsden CD, Fahn S (eds.).
Movement disorders 3. Boston: Butterworth, 1994: 373-405


Cross References

Myokymia; Myotonia; Neuromyotonia; Paramyotonia; Rigidity; Spasticity