The abdominal reflexes are superficial reflexes in which a light stroke across the skin of each quarter of the abdomen makes the underlying muscles contract and pull the umbilicus toward that side. The upper reflexes test about T8-T10 and the lower reflexes about T10-T12. They are carried by the lower intercostal and subcostal nerves.
| Nerve root | T8-T12 |
|---|---|
| Area | Skin of the four abdominal quadrants, stroked toward the umbilicus |
| How to test | With the patient lying relaxed, the examiner lightly strokes the skin of each quadrant from outside toward the umbilicus and watches the umbilicus move toward the stimulus. |
| Muscles | |
| Nerve Supply | Intercostal nerves (T8-T11); Subcostal nerve; Iliohypogastric nerve |
Protects the abdominal contents by tensing the abdominal wall in response to skin stimulation, and reflects the integrity of the corticospinal tract.
Loss of abdominal reflexes on one side, with other upper motor neuron signs, suggests a corticospinal tract lesion; early loss is a recognised finding in multiple sclerosis. They are often absent in healthy people with obesity, after pregnancy or abdominal surgery, and in older age, so absence alone is of limited value. Absent reflexes in a child with scoliosis can point to a syrinx.
Abdominal reflexes are frequently lost early in multiple sclerosis because of corticospinal tract damage.
A fluid-filled cavity in the spinal cord can abolish abdominal reflexes, sometimes found when investigating scoliosis.
A lesion at the T8-T12 levels abolishes the reflexes supplied below it.
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