Sympathetic skin response: a new test to diagnose erectile dysfunction

Guang-You ZHU, Yan SHEN

Institute of Forensic Sciences, Ministry of Justice, China, Shanghai  200 063, China. 

Asian J Androl  2001 Mar; 3:  45-48

Keywords: penis; sympathetic nerve system; erectile dysfunction; electric stimulation; median nerve

Abstract

Aim: Electrophysiological monitoring of the activity of the penile sympathetic skin responses (PSSR) in healthy men and patients with erectile dysfunction (ED). Methods: PSSR were recorded from the skin of penis with disk electrodes at the time of electric stimulation of left median nerves. Results: PSSR were recorded from all the healthy men and almost all the patients. In healthy men the latency of P₀, the latency of N₁, the duration of N₁ and the amplitude of N₁ were 1249111 ms, 2239286 ms, 1832505 ms and 470 V (median), respectively. In ED patients the latency of P₀, the latency of N₁, the duration of N₁ and the amplitude of N₁ were 1467183 ms (P<0.01), 2561453 ms (P<0.05), 2560861 ms (P<0.01) and 91 V (P<0.01), respectively. The normal latency of P₀ was less than 1471 ms. The normal amplitude of N₁ was more than 235 V. According to this normal value, of 20 patients 11 showed longer latency of P₀, and 14 showed lower amplitude of N₁ as compared with those of normal subjects. Conclusion: PSSR can be used as an electrophysiological method in assisting the diagnosis of ED.

1 Introduction

2 Materials and methods

2.1 Subjects

Thirty healthy subjects, 24-50 (mean 32) years old, with normal penile erection and without any neuropathy. Twenty patients, 22-55 (mean 31) years old, with erectile dysfunction (11 occured after pelvic fractures with injury of urethra, 3 after severe injury of the perineum, 1 after fracture of the cervical spine, 1 with hypertention, 2 with a history of severe masturbation, and 2 without known causes).

2.2 Examination technique

Subjects were kept in a prone position and were encouraged to relax. The ambient temperature was controlled at 25-28 and ambient noise was kept low. Small silver disk electrodes 1 cm in diameter were applied to the skin of the penis to record the sympathetic skin response. The reference electrodes were placed on the left iliac crest. A pair of disk electrodes, 1 cm apart, was applied to the left median nerves at the wrist. The ground electrode was put on the inner side of the left elbow. Randomly timed stimuli between 40-90 mA, continuing for 0.1 s, were given at internals of 15 s. PSSR were recorded with a Cadwel Excell Evoked Potential System under the condition of band pass 0.1-100 Hz, and amplification sensitivity 250 V/DIV. Five to ten successive responses were obtained from a series of graded stimuli, ranging from about 40 mA (minimal stimulus) to about 90 mA (maximal stimulus), in each subject. When no response was obtained upon a maximal tolerable stimulus, it was regarded as absent response.

2.3 Analysis index

Figure 1. Analysis indices.

2.4 Statistical analysis

3 Results

3.1 Characteristics of PSSR from normal subjects

PSSR was easily recorded in all the normal subjects. It is a biphasic wave with an initial negative followed by a positive wave (Figure 2). Usually PSSR can be evoked by low intensity stimuli of 10-30 mA. Its latency decreased and amplitude increased when the intensity of stimuli increased within a certain range.

Figure 2. Normal PSSR from a normal subject.

3.2 Characteristics of PSSR from abnormal subjects

The contour of the PSSR from abnormal subjects was the same as that of normal subjects, but with longer latency, much lower amplitude and longer duration than those of normal subjects (Figure 3).

Figure 3. Abnormal PSSR from a patient.

Its latency was also decreased and amplitude increased as the intensity of the stimulus was increased within a certain limit (Figure 4).

Figure 4. Abnormal PSSR from an ED patients.

3.3 Analysis indices of PSSR in general (Table 1)

Table 1. Analysis indices of PSSR.

AN₁: median amplitude; Normal values: described in text

3.4 Analysis indices of PSSR in patients (Table 2)

According to the normal values from the normal subjects, LP₀, LN₁, and AN₁ were abnormal in 11 (55%), 5 (25%) and 15 (75%) of the 20 patients, respectively. There were different abnormalities in the patients with different diseases.

Table 2. No. of abnormal cases in PSSR and other tests.

PEPs=pudendal evoked potentials^[5]; NPT=nocturnal tumescense test^[6].

4 Discussion

The latency of SSR includes afferent and efferent conduction time and central pr ocessing time. The SSR can be evoked by many types of stimulation, such as sound and electricity. Although the ascending time is varied with the type of the stimulation, the latency difference is less than 5% with different stimulations, therefore, this difference can be neglected. The central processing of the sensory information is quite complicated and is not clear yet. The process involves the central sense-motor cortex, especially the premotor areas, the hypothalamus, the limbic system, the basal ganglei and the reticular formation. Their efferent fibers form the sympathetic and sudorimotor neural fibers which travel along the ipsilateral spinal cord and change their neurons in the lateral horn, then innervate the neuroglands^[1]. In healthy persons, sensory or emotional stimuli may excite the autonomic system, inducing a decrease in skin electrical resistance and changes in electric potentials. Therefore it is believed that the SSR is associated with the activity of sweat glands.

The sympathetic skin response consists of 2 types of responses, the palmar and the plantar SSR^[7,8].  When the median nerve is stimulated electrically, excitatory impulses arise in the brain. These impulses descend through the spinal cord, and some enter the sympathetic trunk at the level of T2 to T8 and reach the palm via the brachial plexus to produce the palmar sympathetic skin response. Some enter the sympathetic trunk at the level of T11 to L3 and reach the sole via the sciatic nerve to produce the plantar sympathetic skin response. On the other hand the sympathetic sexual impulses emerged in the brain descend through the spinal cord and enter the sympathetic trunk at the level of T11 to L2. Then they further descend via the hypogastric nerve, pelvical plex and then cavernosus nerves to the penis.

Previous studies have showed that the palmar and plantar SSR could be recorded in all normal subjects by different stimuli, such as sound, electricity or respiration. It is reported that there were no significant differences in the latency of SSR with different types of stimuli. It is believed that SSR is a multiple synapse potential with long latency and regulated mainly by the cerebral cortex. This is one of reasons that the latency of SSR is not dependent on the types of stimuli^[9]. It has been reported that SSR is not related to the age, height and sex of the person^[9,10].

Since the sympathetic fibers innervate the whole skin of the body, we believed that SSR could be recorded from the skin of the penis and the PSSR could reflect the functional state of the automatic nervous system associated with penile erection. Actually, our study revealed that all subjects with normal erection showed a PSSR, which is characterized by a shorter latency and higher amplitude. While ED patients showed a PSSR characterized by a longer latency and lower amplitude. It is found that the threshold of the stimulation for PSSR is about 5-10 mA. With increasing  stimulus intensity, the latency of PSSR is decreased and the amplitude increased. When the stimulation intensity is increased to a given level the latency of PSSR will no longer decrease and amplitude no longer increase. Accordingly, a stable PSSR can be recorded by increasing the stimulation intensity to a certain limit.

Park et al^[4] studied 10 individuals with normal erectile and ejaculatory function and reported that the palmar and plantar sympathetic skin responses were obtained in two ED patients with normal ejaculatory function. Of the 3 patients with ejaculatory dysfunction and normal erection, 2 lacked both SSR and 1 showed both SSR. Of 9 patients with erectile and ejaculatory dysfunction, 7 lacked the palmar SSR and all 9 lacked the plantar response. In the present study, it is shown that in 20 ED patients, 2 lacked PSSR and 18 showed PSSR with a longer latency and a significantly lower amplitude. Park et al^[4] also studied 4 patients with spinal cord lesion and 1 with ED. Of the patients with normal ejaculatory function 2 could ejaculate by masturbation without full erection of the penis. The palmar and plantar SSR were demonstrated in all cases. The latency of the SSR was relatively longer in this group than in normal subjects. In 7 patients with spinal cord lesions, 3 had diabetes mellitus, 1 underwent a pelvic operation and 1 had idiopathic loss of ejaculation. Of these 12 patients 9 also had ED. No plantar SSR was obtained in this group except for 1 patient who had had a pelvic operation for rectal cancer. The palmar SSR were induced in 3 patients. Neither a palmar nor a plantar SSR was obtained in the other 9 patients. The latency of the SSR that could be elicited was within the normal range. The bulbocavernosus reflex was absent in 3 patients, and its latency was normal in 7 and prolonged in 2.

In the present study we found that in the 20 patients with ED, 10 showed longer latency (50%), and 15 showed lower amplitude (75%). Of the 11 patients with pelvic fracture and urethral rupture, 5 showed prolonged latency (45%), 7 showed lower amplitude (64%), 4 showed abnormal pudendal evoked potentials (36%), and 3 showed abnormal NPT (27%). In the other patients, some showed abnormal latency and amplitude, but the pudendal evoked potentials were normal.

The results of the present study suggested that PSSR is a new electrophysiological method for assisting the diagnosis of ED.

References

[1] Schwalen S. Peripher autonome potentiale (PAP) in der neurologishen diagnositik, In: Joerg J, Hielscher H, editors. Evozierter Potentiale in Klinik und Praxis. Berlin, Heidelberg: Springer-Verlag; 1993.
[2] Christie MJ. Electrodermal activity in the 1980's, A review. J Roy Soc Med 1981; 74: 616-22. 
[3] Baba M, Watahiki Y, Takebe K. Sympathetic skin response in healthy man. Electromyogr Clin Neurophysiol 1988; 28: 277-83.  
[4] Park YC, Esa A, Sugiyama T, Kaneko S, Kurita T. Sympathetic skin response: a new test to diagnose ejaculation dysfunction. J Urol 1988; 139: 539.
[5] Zhu GY, Shen Y. Application of pudendal evoked potentials in diagnosis of erectile dysfunction. Asian J Androl 1999; 1: 145-50.
[6] Zhu GY, Wu J, editors. Forensic Adrology in Practice. Beijing: Law Publishing House; 1988.
[7] Elie B, Guibeneue P. Sympathetic skin response: normal results in different experimental conditions. Electroencephalogr Clin Neurophysiol 1990; 76: 258-67.
[8] Toyokura M. Waveform variation and size of sympathetic skin response: regional  difference between the sole and palm recordings. Clin Neurophysiol 1999; 110: 765-71.
[9] Wang JJ. Analysis of sympathetic skin response of 83 normal subjects. J Clin Electroencephalogra 1997; 6: 201-3.
[10] Wang JJ, Zheng ZL. Sympathetic skin response. J Clin Electroencephalogra 1999; 8: 121-3.

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Correspondence to: Dr Guang-You ZHU, Institute of Forensic Sciences, Ministry of Justice,  China, Shanghai 200 063, China. 
Tel: +86-21-6204 2598    Fax: +86-21-6244 2691 
e-mail: chendj@online.sh.cn
Received 2000-10-08     Accepted 2001-02-01