European Urology European Urology 42 (2002) 281±288 ModulationofViscero-Somatic H-reflexduring Bladder Filling: APossibleToolinthe Differential Diagnosis of NeurogenicVoiding Dysfunctions A. Carbone a,* , G. Palleschi a , R. Parascani a , P. Morello a , A. Conte b , M. Inghilleri b a Department of Urology, University of Rome ``La Sapienza'', Policlinico Umberto I, Viale del Policlinico, Rome, Italy b Department of Neurology, University of Rome ``La Sapienza'', Policlinico Umberto I, Viale del Policlinico, Rome, Italy Accepted 12 June 2002 Abstract 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 ®lling 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 in¯uence of bladder ®lling on somatic re¯exes, we studied the H-re¯ex evoked by electrical stimuli applied to the tibial nerve at the popliteal fossa and recorded from the soleus muscle. The H-re¯ex was tested in the following conditions: (1) empty bladder; (2) medium bladder ®lling; (3) maximum bladder ®lling; (4) ®ve minutes after bladder emptying. The H-re¯ex amplitude at empty bladder was considered as the control value. Results: In healthy subjects, we observed a progressive reduction in the H-re¯ex amplitude during bladder ®lling. In spinal cord-injured patients affected by a neurogenic overactive bladder, bladder ®lling failed to inhibit the H-re¯ex amplitude; a decrease in the H-re¯ex amplitude similar to that displayed by normal subjects was observed in patients with a non-neurogenic overactive bladder. By contrast, H-re¯ex behavior was unmodi®ed in neurogenic underactive bladder patients and was similar to normal subjects in psychogenic underactive patients. Conclusions: As behavior of the H-re¯ex varies during bladder ®lling in neurogenic and non-neurogenic overactive bladder patients as well as in neurogenic and non-neurogenic underactive bladder patients, H-re¯ex modulation may be considered a useful tool in the differential diagnosis of voiding dysfunctions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Neurogenic bladder; Bladder proprioception; H-re¯ex 1. Introduction The neurophysiological control of the bladder is particularly complex, involving both the peripheral and central nervous systems at different levels. Many of the neuronal mechanisms involved during the ®lling and voiding phases are fairly well known. Bladder distension causes a gradual increase in pelvic nerve afferent ®ring; when the micturition threshold is reached, pelvic nerve afferent ®ring activates the effer- ent pathways which are switched on and burst for a short period, thereby determining bladder contraction and consequent micturition [1±3]. The micturition re¯ex is thought to be due to the activation of afferent unmyelinated C ®bers and the ®nely myelinated A delta ®bers of pelvic nerves connected to the slowly adapting mechano-receptors of the bladder wall [2,4,5]. Several studies have shown that neurons receiving input from the urinary bladder, such as spinal cord cells, are connected to supraspinal structures involved in the control of the micturition re¯ex. The spinal cell threshold is in¯uenced by small rises in bladder pres- sure, the ®ring rate being increased by vesical pressure * Corresponding author. Tel. 39-644-231-005; Fax: 39-644-231-005. E-mail address: antonio.carbone@uniromal1.it (A. Carbone). 0302-2838/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0302-2838(02)00309-3