Low back pain that goes down the leg is often divided into two groups: radicular and pseudoradicular. Radicular suggests that pressure on the nerve root causes neuropathic pain. This type of pain travels along the nerve pathway down past the knee.
Pseudoradicular means like radicular pain but it’s not the same. The pain goes down the leg to the knee, but doesn’t go past the knee. The source of the pain isn’t pressure on the nerve. Instead, there is a mechanical cause. This could be from degenerative or inflammatory joint changes.
Treatment of the problem is based on an accurate diagnosis of the source of the pain. Special tests are performed to place patients in one of two groups. But there’s been some question about the real differences between these two groups.
In this study, a special battery of tests called Quantitative Sensory Testing (QST) is used. QST measures sensory stimuli including cold, warm, pinprick, pressure, touch, and vibration. Patients in three groups were tested. Results were compared between patients with radicular vs. pseudoradicular pain. The third group was a control group of healthy subjects without back or leg pain.
Most of the patients in the radicular group had sensory deficits as measured by the QST. They also had a loss of motor function in the foot. This symptom corresponds with the sensory changes observed. These findings confirm the pain is neuropathic in origin.
Some sensory deficits were also detected in the pseudoradicular group. These were milder or subclinical, meaning patients with pseudoradicular pain weren’t aware of any loss of sensation. The authors suggest this points to possible nerve fiber damage that hasn’t been unrecognized in pseudoradicular low back pain.
The results of this study show the need to treat both neuropathic and mechanical low back pain in some patients. The term mixed pain may be applied to this group.
The authors discuss the specific nerve fibers affected by radicular versus pseudoradicular pain (e.g., myelinated, unmyelinated, large, small, C-fibers). They suggest pseudoradiculopathy and radiculopathy are two types of the same problem. Each is on a continuum rather than two separate conditions. It’s important to make the distinction because treatment must address each problem differently.