Electrophysiological evaluation of the stiff-man syndrome: Further data

Abstract

Sirs: We read with interest the paper by Meink et al. [18] concerning the neurophysiological evaluation of the stiff-man syndrome (SMS). The authors found in SMS a peculiar form of myoclonic jerking, termed spasmodic reflex myoclonus, as well as abnormalities of segmental and suprasegmental reflex organization. They speculated that the stiffness of SMS is a fragment of spasms, hypothesizing, as a common neuronal mechanism, a dysfunction of the interneurons of the spinal grey matter. These data have prompted us to report the neurophysiological study of a new case of SMS. To our knowledge, two of the reflex activities examined have not previously been evaluated in SMS. A 63-year-old farmer complained, from the age of 48 years, of episodic stiffness of lumbar axial muscles culminating in painful spasms of the lower right limb, triggered by emotional stimuli. From the age of 50 the stiffness spread to the controlateral lower limb, truncal, upper limb and neck muscles, hindering voluntary movements; painful spasms worsened in frequency, intensity and duration triggered also by mechanical and sensory stimuli. Neurological evaluation showed no abnormalities in the short-lasting inter-spasm periods, but gentle skin stimulation, a sudden noise, or an emotional input triggered a diffuse painful muscular spasm. During the spasm the spinal hyperlordosis worsened, and the patient's voluntary movements were severely limited; he assumed a "wooden soldier" appearance. Neuropsychological assessment was normal. The administration of 35 mg/day diazepam reduced the spasms; plasma exchange followed by steroid administration permitted us to taper the dose of diazepam to 5 mg/day. Extensive laboratory evaluation revealed normal values except for positive antibodies directed against glutamic acid decarboxylase in the serum. Brain CT and MRI were normal. Needle EMG examination of a pair of antagonistic muscles (quadriceps and biceps femoris, tibialis anterior and soleus) revealed a "spontaneous" activity composed of normal motor unit action potentials firing asynchronously. A full recruitment pattern of 2.5-3 mV amplitude during maximal effort was observed. However, it provoked diffusion of the contraction to the ipsilateral and contralateral muscles. With a tactile, acoustic or emotional stimulus, the contraction increased markedly and became painful, while the administration of 10 mg diazepam i.v. abolished both the spontaneous activity and the effects of exteroceptive stimuli. Motor and sensory nerve conduction evaluation of four nerves (right median and peroneal, left ulnar and tibial) disclosed normal conduction values for the patient's age. The silent period was determined in the tibialis anterior muscle during a voluntary contraction stimulating the peroneal nerve at the head of the fibula by an electrical shock of 0.1 ms duration. An H reflex with a normal latency was obtained from the soleus muscle. The H-M recruitment curve showed a normal shape, as did the H-H recovery curve by paired shock [conditioning stimulus 0.8 of the motor threshold (MT) test stimulus = Hmax/2]. The H/M ratio was normal, i.e. 0.45. The polysynaptic flexion reflexes RII and RIII of the short head of the biceps femoris muscle [8] and extension (RPPS) of the soleus [15] were P. Pa. 60 yrs