1 Introduction

Some objective tools have recently been developed in order to differentiate the nature of erectile dysfunction, i.e., nocturnal penile tumescence (NPT)^[1,2], electrically induced bulbocavernosus(BC) reflex^[3], penile blood pressure, Doppler sonography, and plethysmography of penis^[4,5]. These new objective aids will probably reveal increasing cases of erectile dysfunction due to organic causes, especially those of neurological origin. Recent trends indeed, have shown that erectile dysfunction is not uncommon in male patients with diseases of the nervous system^[6,7].

2 Materials and methods

2.1 Subjects

One hundred adult healthy males (Han race, mean age=38 years old) without any known neurological disorder and 84 patients (Han race) having erectile dysfunction alone or in conjunction with various diseases, were investigated. Of these patients, 31 cases developed erectile dysfunction after pelvic fracture(mean age=31 years old),10 after spinal injury (mean age=42 years old),16 with diabetes(mean age=50 years old) and 27 have a history of masturbation more than 5 years(mean age=31 years old).

2.2 SEPs: stimulating and recording methods^[8]

The dorsal nerves of the penis were stimulated via 2 ring electrodes, 1.5 cm apart, wrapped around the penile shaft, with the cathode placed proximally. The response was bipolarly recorded at the spinal level (Th12-L1) and from the scalp, roughly overlying the sensorimotor cortex for the genital region (2 cm behind Cz, referred to Fz of the international 10-20 system). The subject was asked to relaxedly lie down on a bed at a supine position. Stimuli consisted of rectangular pulses 0.1 ms in duration, 3-4 times above the subjective threshold and a 2.77/s repetition rate. The subjective threshold was defined as the lowest perceivable intensity. The tracing represented the final average of 250 artifact-free responses. This gave reproducible SEPs in a reasonable time. The latency of the spinal response was measured at the peak of the initial negative deflection(sensory peripheral conduction time=sensory PCT). The latency of the scalp SEP was taken at the first reliable positive peak(wave P40=sensory total conduction time=sensory TCT). By subtracting the former from the latter, the sensory central conduction time (sensory CCT) was obtained.

2.3 MEPs: stimulating and recording methods^[8]

Brain and sacral root stimulation was performed with simultaneous recording of the response in BC muscle with surface electrodes. Three different motor conduction times were determined: a motor total conduction time (motor TCT) which represents the transit time from brain to target muscle, a motor peripheral conduction time (motor PCT) which corresponds to the sacral roots to the target muscle transit time and, by subtracting the latter from the former,a motor central conduction time (motor CCT=brain to sacral roots conduction time) was obtained. Stimulation was performed via a magnetic stimulator (Cadwell MES-10) with a coil of 9 cm internal diameter applied in direct contact to the skin. The intensity of magnetic stimulation can  be expressed as a percentage of the maximum (=2.5 Tesla). The stimulation was performed with the posterior edge of the coil applied 2 cm behind Cz. First,the stimulation intensity was progressively increased until an MEP could be recorded in the muscles with the subjects at rest. The transcranial stimulation was then repeated with the same intensity during a transient and moderate voluntary contraction of the examined muscles (facilitation procedure). Spinal root stimulation was performed with the center of the coil applied 5 cm laterally to the spine at the level of the right iliac crest. MEPs were recorded only at rest. Latencies were measured at the onset of the first steady deflection from the baseline.

Both SEPs and MEPs were obtained with a poststimulus analysis time of 100 ms and 50 ms, respectively, and a filtering bandpass of 10-500 Hz. They were repeated several times and superimposed to facilitate discrimination of stimulus locked from random activity. A relative negativity in grid 1 of the amplifier provoked an upward deflection.

2.4 SRL: stimulating and recording methods^[8]

3 Results

3.1 Healthy subjects

SEPs: The cortical response had a ‘w’-shaped wave form. The mean latency of the first positive peak (P1) measured as total sensory conduction time (TCT) was 39.73 ms (+3s=45.82 ms) (Table 1).

Table 1.Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) of 100 healthy adult males (latencies in ms)