MS is a chronic, immune-mediated disease targeting the central nervous system, including the brain and spinal cord. While MS is primarily known for affecting mobility, vision, and sensation, many individuals ask about its potential effects on other organs, such as the kidneys. The relationship between MS and kidney health is not a direct immune attack on renal tissue. Instead, it is an indirect consequence of neurological damage, primarily involving the lower urinary tract and the treatments used to manage the condition.
The Primary Connection: Neurogenic Bladder
MS lesions damage the myelin sheath on nerve fibers, often occurring in spinal cord and brain regions that control bladder function. This neurological damage disrupts communication between the central nervous system and the bladder muscles and sphincters. The resulting condition is called neurogenic bladder dysfunction, which affects a large majority of individuals with MS, with estimates as high as 80 to 90 percent.
This dysfunction typically manifests in two ways, which often co-occur. One type is an overactive bladder, where the detrusor muscle contracts involuntarily, causing urgency, frequency, and incontinence. The second type involves underactivity or a lack of coordination between the bladder muscle and the external sphincter, known as detrusor-sphincter dyssynergia. This discoordination prevents the bladder from emptying completely, leading to a build-up of residual urine.
The core issue linking MS to potential kidney problems is the inability to fully empty the bladder, known as urinary retention. Interrupted nerve signals prevent the bladder from coordinating the muscle contraction and sphincter relaxation needed for a complete void. This neurological cause of bladder issues creates the risk for serious complications affecting the upper urinary tract and kidneys.
Kidney Damage Resulting from Bladder Dysfunction
The main risk to the kidneys arises from the physical and infectious consequences of chronic urinary retention caused by neurogenic bladder. Stagnant urine acts as a reservoir for bacterial growth, significantly increasing the risk of recurrent Urinary Tract Infections (UTIs). If these lower tract infections are not treated promptly, they can ascend the ureters to the kidneys, causing a severe infection known as pyelonephritis.
A second mechanical threat to the kidneys is high bladder pressure. In cases of detrusor-sphincter dyssynergia, the bladder muscle attempts to contract against a closed or poorly relaxed sphincter. This elevated pressure can force urine backward up the ureters toward the kidneys, a condition called vesicoureteral reflux (VUR).
The constant back-pressure can also lead to hydronephrosis, which is the swelling of the renal pelvis and calyces due to urine backup. Over time, the combination of recurrent infections and sustained high pressure can cause scarring and progressive damage to renal tissue. This cumulative damage can eventually impair the kidney’s filtering capacity, potentially leading to chronic kidney disease. While the rate of significant kidney deterioration is low, the process can be slow and may only be detected after many years.
Medication and Treatment Considerations
Beyond the indirect effects of MS, some medications used to manage the disease can influence renal health. Disease-Modifying Therapies (DMTs) alter the course of MS, but some are metabolized or excreted by the kidneys. Certain oral or injectable DMTs, such as alemtuzumab, have been associated with a higher risk of chronic kidney disease and require careful monitoring of renal function.
The immune-modulating effects of some DMTs, including interferon-beta, have also been linked to specific kidney conditions like glomerulonephritis. Glomerulonephritis involves inflammation and damage to the kidney’s filtering units. Therefore, a patient’s pre-existing renal function must be assessed and tracked closely when initiating or continuing a DMT.
Symptom management drugs, often used to control bladder issues or pain, also warrant consideration. Medications like anticholinergics reduce bladder overactivity, but they can sometimes worsen urinary retention. This indirectly increases the risk of infection and back-pressure on the kidneys. Additionally, the long-term use of over-the-counter pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can strain the kidneys and potentially contribute to damage.
Monitoring and Protecting Kidney Health
Given the potential for both disease-related and medication-related renal risks, proactive monitoring is an important part of MS management. Regular blood tests assess kidney function by measuring serum creatinine, blood urea nitrogen (BUN), and the estimated Glomerular Filtration Rate (eGFR). These tests indicate how efficiently the kidneys are clearing waste products from the blood.
Routine urinalysis checks for signs of infection, blood, or protein in the urine, which can signal damage or inflammation. For individuals with established bladder dysfunction, management strategies protect the upper urinary tract from pressure and infection. Effective bladder emptying, often achieved through techniques like clean intermittent catheterization (CIC), is the primary method to prevent residual urine and associated risks.
Maintaining adequate hydration is also important, as it helps flush the urinary system and dilutes bacteria, reducing the likelihood of a UTI. Regular consultation with a healthcare provider, including a neurologist and urologist, ensures bladder management is optimized. Consistent monitoring allows for timely intervention, which minimizes the risk of long-term renal complications.