Evaluation of Botox Treatment on Chronical Scrotal Pain

Background:

Chronic scrotal pain (CSP) is a common condition with a prevalence of 2.5-4.8% in male outpatients. Up to 40% of these patients report depressive symptoms and many feel isolated.

CSP is defined as intermittent or constant unilateral or bilateral scrotal pain with a significant impact on the patients daily life. The etiology of CSP is not fully understood but can be related to surgical procedures such as vasectomy, inguinal hernia repair, scrotal surgery and abdominal and groin surgery, even though no apparent cause can be identified in 25-50% of the cases.

When no obvious source of pain is found the most common approach usually begins with conservative treatment including analgesia, antibiotics and in some cases anticonvulsants and antidepressants. When conservative treatment fails, a minimal invasive procedure with local anesthesia cord block is often used before more invasive treatments such as denervation, vasovasostomy, orchiectomy or epididymectomy.

Of the minimally invasive procedures, spermatic cord block has proven to significantly reduce pain briefly in patients with CSP. Because of these findings, it has been proposed that a longer-lasting effect could be obtained with the use of OnabotulinumtoxinA (BTX). BTX is widely used in pain management in many painful diseases such as chronic pain syndrome, myofascial syndrome, headaches, arthritis, and neuropathic pain.

BTX interfere with neural transmission by blocking the release of acetylcholine, the principal neurotransmitter at the neuromuscular junction, causing muscle paralysis. Function can be recovered by the sprouting of nerve terminals and formation of new synaptic contacts which usually takes two to three months.

The use of BTX in patients with CSP have had varying results. One open-label study by Khambati et al reported a significant reduction in pain measured by VAS-score at follow-up after one and three months, but pain and tenderness had returned to baseline after six months. The only randomized double-blinded study by Dockray et al. showed no significant reduction in pain measured by VAS-score at follow-up after one month.

The aim of this study is to investigate the effect of chemical denervation with BTX injections on pain in patients with CSP.

Methods

Study population and recruitment Patients with CSP will be included according to the inclusion and exclusion criteria's (table 1). The following variables will be considered: gender, age, length of symptoms, and questionnaires, e.g., quality-of-life questionnaire (EQ-5D-5L) and Chronic Prostatitis Symptom Index (NIH-CPSI).

Determination of sample size Given that the true success rate for BTX, regarding the primary endpoint, is at least 0.70, and the placebo success rate among controls is 0.20. The investigators will need to study 23 experimental patients and 23 control patients to be able to reject the null hypothesis that the failure rates for experimental and control subjects are equal with probability (power) 0.9. The type I error probability associated with this test of this null hypothesis is 0.05. Considering potential dropouts, the investigators will include 25 patients per group.

Investigations Patients with CSP will undergo a comprehensive workup: including a thorough medical and psychical history, physical examination (i.e. inspection and palpation of penis, testis, funiculus, groin including inguinal channel, abdomen, direct rectal exploration with evaluation of the pelvic muscles, hips and column), investigations of lower urinary tract symptoms (i.e. uroflowmetry and bladder diary), blood work (i.e. creatinine, hematocrit, white blood cells count and C-reactive protein), Doppler ultrasonography of the scrotum, urine analyze (i.e. urine culture, test for chlamydia and gonorrhea). In case of no apparent cause, conservative treatment will be initiated with paracetamol 1000 mg four times a day, ibuprofen 400 mg three times a day or Prostazocin 2.5 mg three times a day. If no pain relief occurs within 30 days, patients are offered funicle cord block with 10 ml lidocaine 20 mg/ml. In case of a significant decrease in scrotal pain measured by VAS, patients will be offered inclusion in the study according to the study inclusion criteria and after written informed consent is provided.

Prior to BTX cord block patients will answer the following questionnaires:

1. Visual analog score for pain (VAS)
2. Quality-of-life (EQ-5D-5L)
3. Chronic Prostatitis Symptom Index (NIH-CPSI)
4. ICD-10 depression questionnaire (MDI)
5. Likert global assessment scale (L-GAS)
6. International Index of Erectile Function questionnaire (IIEF) Questionnaires will be repeated after 1, 2, 3, 4, 8 and 12 weeks. Physical examination will be repeated after 4, 8 and 12 weeks. Patients will be randomized to the intervention or control group.

In both groups injection of either BTX or sterile saline will be given close to the superficial inguinal ring. The intervention group will receive a solution of 100 IU BTX with 10 ml sterile saline while the control arm will receive 10 ml sterile saline. At the 3 months' time point, patients will be unblinded to the treatment and patients in the control group will have the option of cross-over.

Data analysis Univariate analysis and multivariate analysis will be performed: T-tests will be used to compare means between groups and chi-squared tests to compare dichotomous variables, and to adjust for unequal distribution of parameters at baseline, multivariate regression models, linear models in case of an interval scaled outcome, and logistic regression in case of a dichotomous outcome will be performed.