What do you do with a missing reflex?

What do you do when you cannot elicit the cutaneous trunci reflex in a cat?

Okay, first let's talk about this reflex. The cutaneous trunci reflex (CTR) is used in dogs to evaluate the viability of the thoracolumbar spinal cord. It is really LOOOONG for a typical reflex. As with all reflexes there is a sensory and a motor component to CTR. The sensory input is each segmental spinal nerve from T1 to L6 and the motor output is via the lateral thoracic nerve found at C8-T1. Sensory and motor innervation is bilateral however stimulation of one side can result in a contraction bilaterally. 

How do you perform the CTR?

Simulate the hairs or the skin paraspinal between T1 and L6. I use my fingers, hemostats or in rare cases a needle to gently poke the skin. The sensory information goes through the spinal nerve, ascends the spinal cord to synapse on the nucleus of the lateral thoracic nerve found C8-T1. After synapses the motor efferent lateral thoracic nerve contacts the panniculus or cutaneous trunci muscle and you see a visual twitch. The effect may be bilateral, even if you stimulate unilaterally. 

What is the significance of the CTR in dogs?

When present and complete to L6, it carries no significance. Dogs can have severe spinal cord injury and still have a present CTR bilaterally. HOWEVER, if it is reduced cranial to L6, especially unilaterally, this can help focus your lesion localization in the T3-L3 segment. E.g. - CTR is absent until L1 on the left, the lesion will be 1-2 segments cranial to L1, or the T12-T13 region. What is better than precision?? Tracking lesions! If we take a dog to surgery and remove a herniated disc at T13-L1 and the CTR was cranially advanced to L1 preoperative, I can monitor the CTR for caudal decent to suggest spinal cord healing, or cranial decent to suggest myelomalacia. Perhaps you have seen some of your patients return from spinal surgery with sharpie marks on their back? This is likely due to tracking the CTR.

Terrific, but what about cats?

Cats are well, different, aren't they? To start, the CTR is unreliable. In some cats it is present, in other cats it is not. A recent study published in the Journal of Feline Medicine and Surgery confirmed what most of us suspected clinically: the CTR has no significance in a neurologically abnormal cat. It cannot be used reliably to localize a lesion and it may, or may not, be present regardless of neuroanatomic lesion localization. One more way cats make us smile...

** Paushter AM, Hague DW, Foss KD, Sander WE. Assessment of the cutaneous trunci muscle reflex in neurologically abnormal cats. J Feline Med Surg. 2020.

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