The word spasm implies a sudden, involuntary, muscle contraction, which may be painful (cramp). For example, flexor spasms in patients paraplegic due to upper motor neurone lesions are sudden contractions of the flexor musculature, particularly of the legs, either spontaneous or triggered by light touch. Hemifacial spasm is an involuntary contraction of facial musculature.
Spasm may also refer to a tetanic muscle contraction (tetany), as seen in hypocalcemic states (e.g., main d’accoucheur), tetanus (e.g., risus sardonicus), or tonic spasms of various muscles (e.g., jaw musculature, trismus) which may be dystonic or spastic in origin. Involuntary movements, such as tics, may be known as spasms or habit spasms.
Patients may use the word spasm differently, e.g., to denote paroxysmal sensory phenomena, or even seizures. Infantile seizures consisting of brief flexion of the trunk and limbs (emposthotonos, salaam or jack-knife seizures) may be known as spasms.
Rowland LP. Cramps, spasms, and muscle stiffness. Revue Neurologique (Paris) 1985; 141; 261-273