The anal reflex elicited by cough and sniff: validation of a neglected clinical sign.
BACKGROUND
It is unclear whether contraction of the external anal sphincter (EAS) following a voluntary cough is an integral component of the cough response itself, or a reflex response to the abdominal and pelvic floor dynamics induced by the cough. Clinical experience suggests a reflex origin for this response.


OBJECTIVE
To compare motor latencies for intercostal, abdominal, and EAS muscle contraction after transcranial magnetic stimulation with those following voluntary coughing and sniffing.


METHODS
A needle electrode inserted into the EAS measured responses, which were confirmed by tonic electromyographic recording. Direct motor latencies from the cerebral cortex to the intercostal, rectus abdominis and EAS muscles were obtained using transcranial magnetic stimulation. Sniff and cough induced responses were also recorded in these muscles.


RESULTS
The results suggest that EAS responses following a voluntary cough or sniff represent a polysynaptic reflex.


CONCLUSIONS
As the cough induced anal reflex response is consistent and easily elicited, its use in clinical neurological examination is appropriate.
Chan
C L H
CL
Department of Surgery, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, at the Royal London Hospital, UK.
Ponsford
S
S
Swash
M
M
D000328:Adult; D001003:Anal Canal / Q000502:physiology*; D002540:Cerebral Cortex; D003371:Cough; D004558:Electric Stimulation; D004566:Electrodes; D004576:Electromyography; D006801:Humans; D008280:Magnetics; D008297:Male; D009046:Motor Neurons; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology; D009460:Neurologic Examination; D017773:Pelvic Floor / Q000502:physiology; D011930:Reaction Time; D012018:Reflex / Q000502:physiology*; D012119:Respiration