Discussion
Our patient was likely predisposed to experience severe urinary
retention given her complex medical history. The following basic
physiology is recognized as the scientific basis of severe urinary
retention in the setting of intrathecal opioid administration: the
opioids receptors involved in the urodynamic effects are μ and δ.
Intrathecal opioids acting on opioid receptors in the spinal cord
decrease the parasympathetic firing in the sacral region and decrease
the afferent inputs from the bladder to the spinal cord which results in
an inhibitory modulating effect on the release of acetylcholine that
causes detrusor contraction 6. Some speculate that
there is a dose-dependent mechanism by which intrathecal opioids cause
side effects like urinary retention 1. Other sources
describe a primary dose-independent activation of opioid receptors7. A randomized, double-blind study by Raffaeli et al.
concluded that side effects of intrathecal opioid like urinary retention
can be considered as a patient-dependent effect of the drug, suggesting
the presence of a primary dose-independent excitatory component that
might be related to the theory of the bimodal activation of opioid
receptors. Our case supports this latter theory because dose reduction
did not improve the patient’s severe urinary retention.
The improvement of the patient’s urinary retention was achieved by
changing the type of narcotic. This demonstrates how different narcotics
may vary in how they affect the μ and δ receptors resulting in unique,
narcotic-specific outcomes with respect to pain management and risk of
voiding dysfunction.
Conclusion :
Morphine sulfate was successfully identified as the cause of the
new-onset urinary retention after turning off the morphine IPP. This
patient has a complex medical history including stroke with no residual
deficits, diabetic neuropathy, and peripheral vascular disease that may
have contributed to her susceptibility to severe urinary retention. The
patient’s initial complaint of difficulty urinating and her urodynamic
testing findings may reflect the influence of intrathecal opioid
administration as opioids are known to decrease bladder function by
suppressing detrusor contractility and decreasing the sensation of urge8. Of note, different types of opioids may uniquely
affect bladder storage and emptying demonstrated during urodynamics. For
instance, drugs like fentanyl are more lipophilic than morphine and thus
undergo greater systemic uptake. As a result, there is less rostral
spread in the central nervous system and less influence on storage and
voiding as demonstrated by multichannel urodynamics. Published research
also supports replacing morphine with an alternative narcotic such as
sufentanil in a regional anesthetic regimen to mitigate the risk of
postoperative urinary retention 9. The data indicate
that recovery to normal lower urinary tract function is significantly
faster after intrathecal sufentanil than morphine 6,9.
This case report highlights that chronic pain patients with multiple
comorbidities affecting the nervous system may be uniquely predisposed
to severe urinary retention with IPP use. Intrathecal morphine may be
more likely to precipitate urinary retention in such a patient. We
believe that patients with a morphine IPP in retention should undergo a
trial of an alternative narcotic as a primary management strategy to
resolve the urinary retention and maintain the benefit of the IPP.