A feasibility study examining the utility of sacral dermatomal evoked potentials in assessing urogenital dysfunction

Malladi, Anjaneya Prasad (2024) A feasibility study examining the utility of sacral dermatomal evoked potentials in assessing urogenital dysfunction. Doctoral thesis (DClinSci), Manchester Metropolitan University, in collaboration with University College London Hospitals NHS Trust, London.

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Abstract

Background: Tarlov cysts are cerebrospinal fluid-filled sacs that form in multiple numbers at the location of dorsal root ganglia in the sacral spinal cord region. Tarlov cysts have been known for over seventy years and are often considered benign findings in MRI reports. A group of predominantly female patients suffer from one or more symptoms, such as lower back pain, lower limb pain, sensory disturbance in the perineum, urinary incontinence, constipation, and sexual dysfunction, for no apparent reasons. All these patients have one common feature - Tarlov cysts in their sacral spinal segment. Most of the traditional diagnostic tests are normal in this group. Since all patients with Tarlov cysts do not suffer from these symptoms, traditionally, their presence is often ignored, and patients with urogenital symptoms are investigated for urological, gynaecological, gastroenterological, or spinal causes. Many tests cause more delays in treatment and create economic and psychological burdens on these patients. Studies have shown that patients can get relief from their symptoms after removing Tarlov cysts, which spurred interest in understanding symptomatic Tarlov cysts. It was hypothesised that some Tarlov cysts can interfere with sacral nerve root functions, causing urogenital dysfunction. Aim: To provide objective evidence for sacral root dysfunction in patients with symptomatic Tarlov cysts. Methods: Prospective, cross-sectional observational studies were conducted in three cohorts. In a healthy group (cohort1) study, 20 healthy volunteers (14 women and 6 men) whose age + SD (women: 39+16.6, men:35+10.6), height in cm (women: 162+8.8, men:176+8.1) and BMI (women: 25.9+6.6, men:24.5+5.5) were recruited to generate normative values for the sacral S2, S3 and S4 dermatomal Somatosensory Evoked Potential (dSEP). Regression equations were generated for the cortical latency, amplitude and inter-side differences using independent age, height and BMI parameters. In the spinal cord injury (cohort 2) study, 20 volunteers (13 women and 7 men) had cauda equina-level lesions (18) or thoracic-level lesions (2) confirmed by MRI. Three of the volunteers had an acute onset of symptoms, and the rest had an onset of symptoms ranging from less than a year to over a decade. All volunteers had sensory deficits on their buttocks, the back of their thighs, or in their perineum. The S2, S3 and S4 dSEPs were tested in this group, and the sensitivity and specificity of the sacral dSEPs were established using the Receiver Operating Curve. In the symptomatic Tarlov cyst (cohort 3) study, 20 volunteers (18 women and 2 men) with one or more Tarlov cysts at their sacral spinal cord segment shown in their MRI were recruited. These volunteers were suffering from lower urinary tract symptoms (70%), perineal pain (65%), Persistent Genital Arousal Disorder - PGAD (20%) and paraesthesia in the perineum (15%). Tibial Somatosensory Evoked Potentials (SEP) and Pudendal SEP were also recorded on all volunteers in all three cohorts. The study was approved by the Manchester Metropolitan University Research Ethics and Governance Team (EthOS Reference Number: 46173). Volunteers in all three cohorts were compensated according to the Health Research Authority recommendations (21/NE/0194). Results: Inter-side cortical latency difference is the most useful parameter when considering sacral root dysfunctions. S2 dSEPs have 75% / 70%, S3 dSEPs have 85% / 85%, and S4 dSEPs have 90% / 85% sensitivity/specificity in detecting unilateral sacral root abnormalities.