Shingles, also known as herpes zoster, results when the virus that causes chicken pox reawakens within the roots of sensory or cranial nerves. The primary symptoms of shingles, according to the 2008 edition of "Fitzpatrick's Dermatology in General Medicine," are pain and a unique, one-sided, blistering rash. While most cases affect the trunk or head, shingles occasionally strikes the knee, especially in people who have recently sustained injuries or trauma to the area.
Knee pain from shingles can develop around the same time as a blistering rash, or pain may precede the appearance of the rash by two to three days. In rare cases, shingles occurs in the absence of a rash, a condition doctors call zoster sine herpete.
In uncomplicated shingles, knee pain starts to improve along with the rash, about seven to 10 days for most people, according to the National Institute of Neurological Disorders and Stroke. People with immune system problems such as AIDS or cancer may take longer to heal. In addition, adds NINDS, 6 to 70 percent of people with shingles develop a chronic pain syndrome called post-herpetic neuralgia in which knee pain lasts for months, years or even permanently.
Pain from shingles, according to the 2008 edition of "Harrison's Principles of Internal Medicine," follows the distribution of the affected nerve roots. Sensation to the knee is supplied by nerve roots corresponding to the L4 and L5 levels of the spinal cord. Pain on the inner aspect of the knee or the outer aspect of the thigh suggests the L4 nerve roots. Pain on the outer aspect of the knee and calf or pain that continues diagonally toward the inner aspect of the ankle suggests the L5 nerve root.
Pain that precedes the appearance of the shingles rash is typically described as tingling, burning or increased sensitivity. After the appearance of the rash, pain usually increases and may become debilitating. Patients may describe the pain as stabbing, burning, aching or electrical. Pain may be constant or intermittent. It may be provoked by light touch or other stimuli that would not normally cause pain, or it may occur spontaneously.
Since the knee is an unusual site for shingles pain, the presence of a rash provides an important diagnostic clue. According to "Fitzpatrick's Dermatology in General Medicine," patients should look for 2 to 3 mm, elliptical blisters filled with clear fluid that typically run in parallel with skin folds. The blisters develop on a base of red raised skin that gives them an appearance drops of dew on a flower petal. Many patients confuse the blisters with pimples or, when they are on the knee, with insect bites or razor rash.
According to NINDS, prescription antiviral drugs can decrease the severity and duration of pain from shingles, as well as the risk of post-herpetic neuralgia. Since the drugs work best when started within 72 hours of symptom onset, patients should contact their doctors as soon as possible after they notice something is wrong. For severe pain, a doctor may also prescribe prescription pain killers such as tramadol or fentanil. Steroid are typically reserved for shingles that affects the face--especially the eye, the spinal cord or the brain.
Is This an Emergency?
- "Fitzpatrick's Dermatology in General Medicine, 7th Edition"; K. Wolff et al.; 2008
- "Harrison's Principles of Internal Medicine, 23rd Edition”; A.S. Fauci et al.; 2008
- National Institute for Neurological Disorders and Stroke: Shingles: Hope Through Research
- U.S. Centers for Disease Control and Prevention: Herpes Zoster: Q and A's for Providers