Sympathetic skin response in patients with lateral medullary syndrome

We have carried out a prospective study of the sympathetic skin response (SSR) in 21 patients with lateral medullary syndrome (LMS), with the aim of identifying the most common pattern of SSR abnormalities and its possible correlation with clinical and radiological findings. The amplitude of the SSR recorded in the ipsilateral hand to the infarct was abnormally reduced in the patients as a group. However, using different stimulation and recording sites, and considering only the presence or absence of the response, we identified 5 different patterns of SSR abnormalities: 1. Normal responses; 2. Bilaterally absent responses to stimulation of the ipsilateral supraorbital nerve but not to other stimulation sites; 3. Absent responses in the side ipsilateral to the stroke, with normal responses in the contralateral side; 4. A combination of patterns 2 and 3; and 5. Absent responses to all stimuli. All patients with ipsilateral facial sensory loss had absent SSR to ipsilateral supraorbital nerve stimulation, while there was only a positive correlation between abnormal contralateral facial sensation and preservation of the SSR (Fisher's exact test P=0.003). No correlation was found between the pattern of SSR abnormalities and the infarct topography, assessed with the MRI. Our findings suggest that the damage to the SSR circuits of patients with LMS is not uniform, and follows an heterogeneous distribution independent from the MRI findings, and poorly related to the clinical sensory manifestations.