stiff-person syndrome

noun

variants or stiff person syndrome also stiff man-syndrome or stiff man syndrome

: an uncommon neurological disorder that is marked by progressive muscle stiffness in the spine and limbs and especially the legs and by episodes of painful muscle spasms which occur spontaneously or are triggered by various external stimuli (as a sudden, loud noise)

Note: While the cause of stiff-person syndrome is unknown, it is usually thought to be an autoimmune disorder which affects females more often than males.