Abdominal Reflexes

Level 1: in response to an outpatient teaching session last week.
The abdominal reflexes refers to the reflex stimulated by the stroking of the abdomen around the umbilicus that results in contraction of the abdominal muscles; typically the umbilicus moves towards the source of the stimulation.
How do you perform the reflex?
Stroke the abdomen lightly on each side in an inward direction above and below the umbilicus using a orange stick (wooden stick) or blunt end of a neurotip (figure below). When you do the reflex the patient should be lying down and relaxed with their arms by their sides.

Remember all reflexes have an afferent and an efferent limb; in the case of the abdominal reflexes the afferent is cutaneous sensory (tickle and light touch) that is dermatomal and the efferent limb is the segmental innervation of the abdominal muscles.

I was always taught that the abdominal reflex was a short spinal arc; this however this does not explain why the reflex is typically lost in upper motor neurone syndromes. Loss of the reflex may be abnormal. In contrast, the presence of the reflex is normal.

This reflex is also lost due to a variety of causes, including age, abdominal surgery, obesity, pregnancy and in parous woman. I therefore don't find absent abdominal reflexes a very helpful clinical sign. Their presence on the other hand is very reassuring; particularly when you think the patient has medically unexplained symptoms and signs. In my personal experience the presence of the abdominal reflexes is predictive no significant upper motor neurone pathology. Again don't rely on one sign to make this call; the abdominal reflexes have the be integrated with the remainder of your findings.
The following YouTube video describes and shows how to perform the reflex; this is not how I was taught to do the reflex. I was taught to do only test in 4 quadrants; this demonstration breaks the abdomen up into several sectors; I personally don't think that this is necessary.

Occasionally I have found the abdominal reflexes helpful as a localising sign in patients with thoracic cord lesions; i.e. upper reflexes are intact and the lower reflexes are lost. However, a detailed sensory examination is usually better at localising a specific level than the abdominal reflexes.

Please note that the reflex fatigues or habituates; in other words with repeated stimulation the reflex disappears. So don't be alarmed if your friend finds the reflex and when you try it is not there.

What is the evolutionary role of the abdominal reflexes?

I was taught that the local contraction of the abdominal muscles to an abdominal sensory stimulus was to protect the internal viscera from damage. To test this theory you should try and punch each other lightly in the abdomen; you will soon realise that you can't control the reflex contraction of the muscles.

Extra reading: SPINAL MECHANISM OF THE ABDOMINAL AND ERECTOR SPINÆ SKIN REFLEXES