Lumbar radiculitis: when the scan, the exam and the leg tell different stories.

Sciatica has a clear structural version and a less obvious one. The difference is whether all the evidence points at the same nerve root.

This page is about understanding the condition and the role the brain and nervous system can play in it. It is not a diagnosis. Your own clinicians know your case.

What lumbar radiculitis is

Five pairs of nerve roots leave the lumbar spine and join to form the nerves of the legs, including the sciatic nerve. 'Lumbar' means the low back, and 'radiculitis' means inflammation of a nerve root. When a root is irritated, the person feels pain along the path of that root, down the buttock and the back or side of the leg, sometimes to the foot. There may be numbness or tingling in a strip of skin the root supplies, and weakness in the muscles it controls. This is what most people call sciatica.

The classic cause is a herniated disc that bulges onto the root, or narrowing of the spinal canal. The classic course is also reassuring: most disc-related sciatica improves substantially within six to twelve weeks as the inflammation settles and the disc material shrinks.

The complication is that disc bulges, protrusions and degenerative changes are extremely common in people with no symptoms at all. An MRI will usually find something. The question is whether what it finds explains what you feel.

The neuroplastic contribution

Neuroplastic symptoms are real symptoms generated by learned pathways in the brain and nervous system rather than by ongoing damage or compression in the body. Pain is an alarm the brain produces to protect you. After an episode of genuine nerve-root pain, or sometimes without one, the brain can learn to produce leg pain in response to bending, sitting, lifting or stress, with no nerve being pinched. The pain is real, it is not imaginary and it is not 'all in your head'.

The ATNS Index of Neuroplastic Symptoms treats lumbar radiculitis with unusual precision. It says the symptoms are least likely to be neuroplastic when three things agree: the symptoms (particularly when numbness or weakness accompany the pain), the physical examination, and the imaging all point to the same compressed nerve root. They are most likely to be neuroplastic when those three fail to correspond, especially when the complaint is pain only. The index's own example is a mild compression on the left in a person whose pain is on the right.

What a mismatch looks like in practice:

• Pain on one side, scan finding on the other, or at a different level.
• Pain that does not follow the path of any single nerve root, or that moves around.
• Pain that persists long after the expected healing time, especially if it flares with stress.

Our guides to the three types of chronic pain and chronic back pain and ACT go deeper.

What the research shows

The ATNS index's rule is drawn straight from the imaging literature. A cross-sectional double-blind study compared MRI findings with the symptom complex in prolapsed disc disease. Among 31 central and 23 centrolateral disc protrusions, 20 in each group were in people with no symptoms, confirming how common silent findings are. But when MRI showed a nerve root or foramen actually compromised by a disc, the association with symptoms was very strong, with odds ratios of 41.7 for root compromise and 6.0 for foraminal compromise. Nearly all of those with true root compression had matching radicular pain. In short, a bulge means little; a compressed root that matches the symptoms means a lot.

A feasibility study of bedside sensory testing in people with lumbosacral radiculopathy found sensory disturbances in 82% of patients, and deep pressure testing showed a relatively high rate of hypersensitivity. Nerve-root pain is not only about numbness along one strip of skin; the nervous system's sensitivity itself changes.

Finally, a recent narrative review titled 'Beyond Structural Pathology' examined central sensitization in chronic pain with specific reference to lumbar disc herniation, describing how pain can persist or spread through nervous-system amplification after the original disc problem has resolved or when the structural finding is too small to explain it. It argues that spotting this sensitized pattern takes a combined assessment: questionnaires such as the Central Sensitization Inventory alongside sensory tests like pressure pain thresholds and conditioned pain modulation.

Signs the brain may be part of the picture

• Your pain is on a different side, or at a different level, from the finding on your scan.
• You have pain only, with no numbness or weakness, and the neurological exam is normal.
• Pain flares with stress, worry or the expectation of sitting, more than with sitting itself.

A solution that addresses it

When the evidence points to the nervous system rather than a pinched root, pain and symptom reprocessing is the approach built for it. It combines education about neuroplastic pain, somatic tracking (observing the leg sensation with curiosity instead of dread), reducing fear and the sense of threat, a graded return to bending, sitting and lifting, emotional awareness and expression, and acceptance and commitment skills. Trained clinicians deliver it, and digital programs are making it more accessible.

Cindra is a daily AI companion built around these approaches, with daily check-ins, short practices and plain-language lessons for people whose symptoms have a neuroplastic component. If your sciatica does not match your scan, you can join the waitlist.

What to do next

1. Get a proper neurological examination. A clinician should test your reflexes, strength and sensation and compare them with your symptoms and any imaging. Seek emergency care for new difficulty controlling bladder or bowel, numbness in the saddle area, or rapidly progressing weakness in a leg. Those are signs of serious nerve compression.
2. Ask the three-way question. 'Do my symptoms, my exam and my scan all point to the same nerve root?' If yes, structural treatment and time are the right path. If no, the ATNS index says neuroplastic symptoms are the more likely explanation.
3. Learn what the scan does and does not mean. Common age-related findings are not injuries. Our guide to hurt versus harm helps.
4. Start retraining. Reduce fear, move in steps, and treat flares as sensitivity rather than damage.

This article is for general education and is not medical advice, and it does not diagnose or treat any condition. Persistent symptoms deserve a proper medical assessment to rule out disease or injury before a neuroplastic explanation is considered. If your symptoms are new, changing, or come with red-flag signs such as fever, unexplained weight loss, numbness or weakness, chest pain, or loss of bladder or bowel control, see a clinician promptly.