Cat Pain Pathways: A-delta, C Fibres, 5-Item Score

A cat in pain does not limp or cry; it hides, sleeps more, and stops jumping on the shelf it used to own. The signal travels on two fibre types at very different speeds, 5-20 m/s for the fast one and 0.5-2 m/s for the slow one, and the visible behaviour is the last link in a 4-step chain. A 5-item facial score of 4 or more out of 10 is the most reliable bedside number you can produce at home.

Two classes of drug do most of the work: non-steroidal anti-inflammatories and opioids. Everything else is timing, restraint and observation.

From skin to brain in 4 steps

Transduction happens at the nerve ending, where heat above roughly 45 C, pressure, or a chemical soup from damaged tissue opens ion channels. Transmission carries the impulse along the axon to the dorsal horn of the spinal cord. Modulation happens in that horn, where signals are amplified or gated down. Perception is the cortex deciding it hurts.

Each step is a place to intervene, and each has a different time course. Local anaesthetic blocks step one for 1-6 hours. An opioid acts on step three within 20-40 minutes. A nerve block can silence a whole limb for 8-12 hours after surgery.

A-delta at 5-20 m/s, C at 0.5-2 m/s

The myelinated A-delta fibre is 1-5 um wide and conducts at 5-20 m/s; it carries the sharp, well-localised first pain. The unmyelinated C fibre is 0.3-1.2 um wide and manages 0.5-2 m/s, which is why the dull burning second pain arrives a beat later. On a 1 m path to the spinal cord the difference is roughly 0.1 s versus 1-2 s.

This is not trivia. It explains why a cat that yelps and then settles is not necessarily fine, and why a slow, spreading ache after surgery needs cover for 48-72 hours, not just the first 6.

Fibre	Diameter um	Speed m/s	Carries
A-beta	6-12	30-70	Touch, pressure, hair movement
A-delta	1-5	5-20	Fast sharp pain, cold
C	0.3-1.2	0.5-2	Slow burning pain, itch
Visceral C	0.2-1.0	0.5-2	Bladder, gut and bile duct stretch

Why cats hide it better than dogs

Descending inhibition from the brainstem is strong in cats, and a prey species that shows weakness pays for it. A cat with a fractured pelvis will still eat, use the box and walk 3 m to a sunny spot, then sit still for 20 hours. The behaviour you see is the residual, not the pain.

Watch changes instead of signs: a cat that stops using a windowsill, eats 20% less, or grooms one flank for 10 minutes longer is giving you a number to compare against.

The 5-item facial score

Five features, each scored 0-2, give a total out of 10. Look at the ears (flattened and rotated out), the orbital area (squeezed), the muzzle (tense, drawn back), the whiskers (bunched forward and up), and the head (held low, below the shoulder line). A total of 4 or more usually means pain worth treating.

Score from a photo taken at eye level, 2 minutes after the cat settles, and repeat at the same time of day. The scale was built for acute pain, so use it before and 60-90 minutes after an analgesic to see whether the number moved.

Two classes of analgesia, and how they differ

NSAIDs cut prostaglandin production at the inflamed site, work for 12-24 hours per dose, and are the backbone for dental, orthopaedic and post-surgical pain; the kidney and gut are the organs to protect, so hydration and a blood panel matter before a 7-day course. Opioids act on the spinal and brain receptors, work in 20-40 minutes, and cover severe or visceral pain that NSAIDs do not touch well.

Doses are set by the vet for the individual cat, and never copied from a dog chart: cats metabolise several drugs by a different pathway and a canine milligram figure can be toxic. Gabapentin is often added for nerve pain over 7-14 days. Never give paracetamol, ibuprofen or aspirin on your own.

Chronic pain looks like a behaviour problem

Osteoarthritis affects a large share of cats over 10 years, and the usual first complaint is a litter box accident or a cat that stopped jumping. Signs to count over 2 weeks: jumps per day, height of the highest jump, stairs taken, and time to rise after rest. A 4-6 week trial of analgesia plus ramps, low-sided boxes and 2 heated beds gives a clear answer.

Dental pain is the other chronic source: 70% of cats over 3 years have some periodontal disease, and many eat normally with a painful tooth. A vet dental check every 12 months is the cheap version of this section.

Where the science stops and the clinic starts

No score replaces an exam. Go the same day for a cat that cannot bear weight on a limb, cries when lifted, has a hard swollen abdomen, or cannot pass urine for 12 hours. Within 24 hours for not eating, hiding in a new place, or a sudden change in gait.

Meanwhile, three things help: keep a 2-week behaviour log, learn the 5-item score so you can report a number, and ask what the plan is for 72 hours after any procedure. Owners who bring a count get better pain control than owners who bring an adjective. Reading the white cell count helps when pain comes with fever, and the breed quiz is a quick way to check whether your cat belongs to a breed with more joint or dental risk.

Frequently asked

How can I tell if my cat is in pain?

Score 5 facial features 0-2 each: ears flattened and rotated out, orbital area squeezed, muzzle tense, whiskers bunched forward, head held below the shoulder line. A total of 4 or more out of 10 usually means pain worth treating. Compare against a photo taken at eye level after 2 minutes of settling, and repeat 60-90 minutes after any analgesic to see whether the score moved.

Why do cats hide pain so well?

Descending inhibition from the brainstem is strong in cats and showing weakness is costly for a small predator. A cat with a fractured pelvis will still eat, use the litter box and walk 3 m to a sunny spot, then sit still for 20 hours. That is why changes matter more than signs: fewer jumps, 20% less food, or 10 extra minutes grooming one flank.

Can I give my cat a dog painkiller?

No. Cats metabolise several drugs by a different pathway, so a canine milligram figure can be toxic, and paracetamol, ibuprofen and aspirin are unsafe without veterinary direction. NSAIDs cover inflammatory pain for 12-24 hours per dose and opioids work in 20-40 minutes for severe or visceral pain, with the dose set by a vet for that individual cat.