The first thing to understand about shingles is that it is not a skin disease but, rather, a neurological disease that affects the skin. Shingles is caused by the varicella zoster virus, the same virus that causes chicken pox. When a person catches chicken pox, after the virus has run its course, it lies dormant in the sensory nerves in the skin. In a shingles outbreak, the virus awakens and travels along the nerves, causing inflammation. The inflammation results in severe pain and a rash or lesions on the surface of the skin. The most common sites for a shingles infection are the face, and back--shingles rarely appears on the arms and legs. While shingles usually attacks the sensory nerves in the skin, it can attack other nerves, including the nerves that control the muscles of facial expression and the bladder.
Nerve Control of the Bladder
The urinary bladder is a muscular pouch that collects urine until it is ready to be removed from the body. In a healthy urinary system, there is a series of muscles and sensory nerves that all signal the brain when the bladder is full. These same muscles also send out sensory signals making us consciously aware of the need for elimination. There are also voluntary muscles that allow us to continue holding urine until it is convenient to eliminate. All of these nerves and muscles work together to allow us to urinate in the right place, at the right time. In a neurologically compromised urinary system, signals are not transmitted properly, leading to bladder dysfunction.
Shingles and the Bladder
When a nerve is irritated, as with a shingles infection, it becomes inflamed, which affects the function of the nerve and all structures attached to the nerve. In some instances, nerves become hyperactive and overstimulate the structure. In the case of the detrusor muscle, which controls contraction and emptying of the bladder, overstimulation will result in frequent urination (urinary frequency), a sudden need to urinate (urinary urgency) and leakage associated with urgency (urge incontinence)--all symptoms of an overactive bladder. In other instances, nerve inflammation can disrupt signal transmission, preventing the structure from functioning properly. If inflammation disrupts transmission to the sphincter muscles, the muscles may no longer contract fully, resulting in urine leakage. Or, the muscles may not fully relax, resulting in difficulty urinating. If inflammation disrupts the signals to, or from, the brain the bladder may retain urine, leading to overflow incontinence, infection and even kidney damage.