Urodynamics investigation is the mainstay in evaluating neurogenic bladders, including DSD, in SCI patients. We should keep in mind that the presence of DSD criteria in the urodynamic testing of a patient with unknown spinal cord pathology should address further investigation of spinal cord involvement [9,17]. At the same time, the examiner should be aware that, during urodynamics, a neurologically intact subject may voluntarily contract the external sphincter during detrusor contractions [5].

Cystometry evaluates the filling and storage phases of detrusor function by measuring changes in the intravesical pressure that occur with increases in bladder volume. The normal adult bladder capacity is around 400–750 mL, with bladder pressure not exceeding 15 cm·H₂O during the filling phase. During cystometry, the leak-point pressure (the pressure value at which voiding occurs) is also measured. Whenever this is higher than 40 cm·H₂O, which is common in DSD, it indicates a risk of subsequent renal damage [18,19]. Other abnormal cystometry findings in DSD patients include decreased bladder compliance, which is hazardous for the kidneys [18,19].

In the literature about DSD assessment in SCI subjects, we found a diversity of invasive urodynamic setups either with or without a pressure-flow study. While there is unanimity in the measuring method of intravesical pressure [2,20,21], the disagreement was due mainly to the different techniques employed to obtain and measure the signal to study EUS behavior, either with or without bladder neck involvement.

Urodynamics with VCUG can evaluate BND [5,6,7]. Yalla et al. [6] considered that internal sphincter dyssynergia alone in SCI patients is rarely seen. In Schurch et al.’s [7] research, 44 urodynamics studies from 34 out of spinal shock SCI patients (28 men, 6 women) with upper motor neuron bladders were evaluated. Interestingly they were able to investigate BND and DSD, since their urodynamics framework included pressure transducers in the bladder, bladder neck, and membranous/bulbar urethra. They found BND and DSD were both present in almost all patients with complete SCI above T12, and that paraplegics with incomplete lesions had DSD without BND. Furthermore, all tetraplegics, either complete or incomplete, presented with BND associated with autonomic dysreflexia. According to Schurch, active BND was independent of EUS action. BND would occur when there was a disruption of the inhibitory influence of the parasympathetic system on the sympathetic control in the bladder neck. These findings should raise questions when considering treatment options in patients with complete SCI above T12, where interventions aiming only the EUS might fail. Soler et al. [33] retrospectively studied the outcome predictors of EUS botulinum toxin injection as a therapeutic intervention in 99 adults male suprasacral SCI patients with DSD, and they determined that the presence of a BND in VCUG was a predictor of failure for this intervention.

In 1986, when diagnostic ultra-sound technology was in its early stages, Perkash et al. used combined urodynamics and transrectal sonography, which they found instrumental in their understanding of neurogenic voiding dysfunction, as well as the role that DSD plays [34]. In our PubMed/Medline search, we found only three other articles, all dating back to the 1980s, related to the simultaneous use of urodynamics and transrectal ultrasound [35,36,37]. Shapeero et al. [36] explored the bladder neck and urethra functions of 32 men with suspected bladder neuromuscular dysfunction using transrectal sonography, urodynamic studies, and VCUG. There were 27 coupled transrectal voiding sonography and urodynamic studies with recordings of periurethral EMG, VCUG, and urethral pressure. Shabsigh et al. [37] performed 31 combined transrectal ultrasonographic and urodynamic studies in 24 suprasacral SCI male patients to study specifically DSD. A variety of urodynamic measurements, including bladder pressure, rectal pressure (obtained from the water-filled condom around the ultrasound probe), detrusor (subtraction) pressure, uroflow, and EUS EMG activity were recorded, and this technique was considered useful in evaluating DSD. Both authors [36,37] found a superiority in diagnostic accuracy of sonography when compared with VCUG, with an advantage/drawback trade-off favoring the ultrasound (an absence of irradiation exposure to the patient and examiner, the potential of imaging the periurethral and bladder soft tissue, and a longer duration of image acquisition). Given the paucity of research results found on urodynamics combined with ultrasound imaging techniques, whose technology has improved exponentially, we searched the literature for other possibilities in this field that might be of interest for the instrumental evaluation of DSD in SCI individuals. Contrast-enhanced voiding urosonography (ceVUS) is a well-established ultrasound method used in children for detecting and grading vesicoureteral reflux, as well as for urethral imaging [38,39]. Notwithstanding, since we did not find any publication on contrast-enhanced voiding urosonography coupled with urodynamics, it seems logical that, at least conceptually, this possibility merits dedicated research in evaluating DSD in SCI patients, especially when electronic pressure sensors will be widely available in urodynamics.

While not specific to DSD, the measurement of the urinary flow rate in an SCI patient with DSD should confirm the presence of bladder outlet obstruction [40]. An intermittent or low flow and the presence of significant PVR in uroflowmetry in a SCI subject is highly suggestive of DSD [8]. In clinical practice, uroflowmetry or important PVR measured by ultrasound, indicating bladder outlet obstruction in an SCI patient, is a noninvasive procedure that should alert the clinician of the likelihood of DSD, fostering further urodynamics investigation. The same argument applies when there is evidence of urine retention in the data from a patient’s bladder or voiding diary, i.e., a daily record of the patient’s bladder functioning which provides an objective documentation of voiding pattern, sensation, volumes (including PVR), incontinence episodes, and events that might lead to an incontinent episode, or urine retention evidence [18]. PVR can also be used as an outcome to appreciate efficacy in DSD treatment [41,42].

2. Other Clinical Dimension in Evaluation of DSD in SCI Patients

2.1. Anamnesis

2.2. Physical Exam

2.3. Complementary Diagnostic and Follow-Up

2.4. Autonomic Dysreflexia and DSD