Pain Recognition and Assessment: Scoring Scales and Species-Specific Behavioral Indicators

Why Pain Recognition Is Difficult

Animals cannot verbally localize or rate their pain, and most species — especially cats — evolved to conceal pain and weakness because expressing vulnerability invites predation. A cat that is hurting will often hide, become silent, and stop grooming rather than cry out. This means a technician who waits for "obvious" pain will systematically under-treat it. The VTNE expects you to understand that the absence of obvious distress does not equal the absence of pain, and that the veterinary technician is the patient's primary analgesic advocate because they spend the most hands-on time with the patient.

Pain is subjective — there is no blood test or objective biomarker. The clinician must infer pain from behavior, physiologic parameters, and response to analgesic trial. For this reason, the gold standard of pain recognition is multidimensional behavioral scoring using a validated tool, applied consistently by the same observer over time.

Behavioral Indicators of Pain

Behavioral indicators fall into several domains. No single indicator confirms or excludes pain — assess the pattern.

Posture

• Hunched or tucked posture — classic abdominal pain sign in both dogs and cats
• "Praying position" (forelimbs down, hindlimbs up) — pancreatic or cranial abdominal pain
• Stiff, reluctant gait — orthopedic or neurologic pain
• Curled tightly, not wanting to move — general discomfort or guarding
• Sternal recumbency with reluctance to reposition — post-abdominal surgery

Vocalization

• Dogs: whining, whimpering, crying, groaning, growling when touched. Absence of vocalization does NOT mean pain-free.
• Cats: vocalization is often suppressed — silence is a red flag. Hissing or low growling when approached is a defensive pain response. Purring is NOT a reliable indicator of contentment — cats purr to self-soothe when stressed, frightened, or painful. Never dismiss pain in a purring cat.

Facial Expression — Grimace Scales

Facial expression scales score discrete facial action units and have been validated as objective, learnable tools:

• Feline Grimace Scale (FGS) — scores five facial action units on a 0–2 scale each (0 = no pain, 2 = obvious change):
  1. Ear position — rotated outward/downward
  2. Orbital tightening — squinting
  3. Muzzle tension — tension around the whiskers and mouth
  4. Whisker position — curled forward or downward
  5. Head position — lowered or tilted Total score ≥ 4/10 (or ≥ 0.4 when normalized) typically indicates pain requiring intervention.
• Glasgow Composite Measure Pain Scale — Feline (CMPS-Feline) — a 16-item or 28-item multidimensional scale combining posture, vocalization, attention to wound, and response to palpation. The short form (CMPS-SF) is most practical in clinical use.
• Canine acute pain scales — the Colorado State University (CSU) Acute Pain Scale is the most widely taught in North America. It is a composite scale combining physiologic parameters, behavioral response to palpation, body tension, and psychological/interactive signs, scored 0–4 with descriptors and an interactive component.

Response to Palpation

Gentle palpation of the surgical or affected site and observation of the patient's reaction is a core pain assessment step. Watch for flinching, lip licking, turning the head, growling, trying to bite, tensing muscles, or attempting to escape. Compare to palpation of an unaffected area.

Appetite, Activity, and Interaction

• Anorexia — common and non-specific but important
• Reduced activity, reluctance to rise, refusal to walk — orthopedic or postsurgical pain
• Self-trauma or licking at a wound — may indicate incisional pain or pruritus
• Hiding (cats especially) — place a box or towel in the cage to allow hiding; a cat that hides more than expected for its recovery stage is likely in pain
• Dull mentation, reduced interaction with caretakers — general malaise/pain
• Inability to settle, frequent repositioning — restlessness is a pain sign, not just anxiety

Validated Scoring Tools Summary

Species-Specific Principles

Dogs

Dogs tend to express pain more overtly than cats — whining, restlessness, guarding, lip licking, yawning, panting out of context. However, stoic breeds (some working dogs) may suppress signs. The CSU scale or CMPS-SF is appropriate.

Cats

Cats are the most under-recognized species. Key principles:

• Hiding and silence are pain signs, not comfort. A cat crouched at the back of the cage, half-hidden under a towel, head down, eyes half-closed, may be in significant pain.
• Provide a hiding place (box, towel tent) — observing whether the cat emerges for food or interaction tells you more than forcing it out.
• Touch the cat gently before scoring — many painful cats appear normal until palpated, then react strongly.
• Use a cat-specific scale (CMPS-Feline, FGS, UNESP-Botucatu). Dog scales miss feline signs.
• Do not interpret purring as contentment — it is a self-soothing behavior.

Other Species

• Horses: grimace scales (Horse Grimace Scale), posture, ear position, response to approach. Horses may become aggressive (ears pinned, swinging hindquarters) when painful.
• Cattle, small ruminants: subtle — ear position, back arching, reduced rumination, teeth grinding.
• Exotics: species-specific; rabbits grind teeth audibly when painful, birds fluff and sit on the cage floor.

The "Trial of Analgesia" and the Analgesic Advocate

When pain status is ambiguous, a diagnostic analgesic trial is appropriate — administer a short-acting opioid (e.g., methadone or hydromorphone) and observe for behavioral improvement over 30–60 minutes. If the patient visibly brightens, eats, relaxes, or interacts more, pain was present and the plan should be escalated. This is the functional definition of the technician as analgesic advocate: observe, score, advocate, treat, and reassess — and never accept a static pain score above the target without intervention.