Modulation of viscero-somatic H-reflex during bladder filling: A possible tool in the differential diagnosis of neurogenic voiding dysfunctions

Objective: Despite evidence that the activation of visceral afferents modulates spinal motoneurone activity in humans, the circuits responsible for this modulation remain unclear. The aim of the present study was to assess the effect of urinary bladder filling on the excitability of somatic spinal motoneurones in patients affected by overactive bladder secondary to neurogenic and non-neurogenic causes in both patients with bladder underactivity and normal subjects by means of a urodynamic evaluation. Methods: In order to evaluate the influence of bladder filling on somatic reflexes, we studied the H-reflex evoked by electrical stimuli applied to the tibial nerve at the popliteal fossa and recorded from the soleus muscle. The H-reflex was tested in the following conditions: (1) empty bladder; (2) medium bladder filling; (3) maximum bladder filling; (4) five minutes after bladder emptying. The H-reflex amplitude at empty bladder was considered as the control value. Results: In healthy subjects, we observed a progressive reduction in the H-reflex amplitude during bladder filling. In spinal cord-injured patients affected by a neurogenic overactive bladder, bladder filling failed to inhibit the H-reflex amplitude; a decrease in the H-reflex amplitude similar to that displayed by normal subjects was observed in patients with a non-neurogenic overactive bladder. By contrast, H-reflex behavior was unmodified in neurogenic underactive bladder patients and was similar to normal subjects in psychogenic underactive patients. Conclusions: As behavior of the H-reflex varies during bladder filling in neurogenic and non-neurogenic overactive bladder patients as well as in neurogenic and non-neurogenic underactive bladder patients, H-reflex modulation may be considered a useful tool in the differential diagnosis of voiding dysfunctions.