Tremors in an Old Cat: 3 Look-Alikes and a 24 Hour Line

Tremor is a description, not a diagnosis. Three patterns look alike in a cat over 11, and 4 questions separate them: was the cat conscious, how long did it last, what triggered it, and what did the body do between episodes. Recording costs 5 minutes per event, and the 24 hour line matters more than a perfect description, because a cat that shakes all day dehydrates in 48 to 72 hours.

The 3 look-alikes

A tremor is rhythmic and fast, roughly 4 to 12 oscillations per second, usually symmetrical, worst when the cat stands or reaches for food, and absent in sleep; the cat stays conscious and can eat. In old cats the common reversible drivers are weakness and electrolyte shifts, low potassium under 3.5 mmol/L, low ionized calcium, high T4, kidney disease, and a toxin. A seizure is not rhythmic: 30 seconds to 3 minutes, loss of consciousness, paddling, salivation, often urination, then 10 to 60 minutes of confusion. Ataxia and vestibular disease are not rhythmic either: a wide stance, a head tilt, drifting to 1 side, falling against the wall, and a cat that is fully awake the whole time.

Under 5 minutes: the recording protocol

Film 30 to 60 seconds, phone at 1 metre, whole body in frame, then 10 seconds of the head close up, with the phone resting on a table and no flash. Write 6 fields: clock time, length in seconds, what the cat was doing at the start, both sides or 1 side, whether the head was involved, and how many minutes until normal. Cap the session at 5 minutes. Handling a trembling cat for longer raises stress, raises body temperature, and produces more shaking that tells you nothing new. If it continues past 5 minutes and the cat is conscious, stop filming, put it on a soft surface at floor level, and call the clinic with the video ready.

The 24 hour line

Call now for a seizure over 5 minutes, 2 seizures in 24 hours, tremor that runs over 60 minutes, a cat that cannot stand, eat or drink, a new head tilt with vomiting, a temperature over 40 or under 37.5 Celsius, or any known exposure to permethrin flea product for dogs, lily, antifreeze, compost or a human medicine dropped on the floor. The window is 24 hours, not a week: an old cat that trembles continuously for a day stops eating, and 2 days of that is a 5 percent weight loss on a 4 kg cat.

The 2 checks a vet starts with

First, blood: complete count, biochemistry, total T4, glucose, ionized calcium, potassium and bile acids, with results in 24 to 48 hours, which catches most of the reversible causes in 1 visit. Second, a neurological exam plus systolic blood pressure, where 160 mmHg is the usual flag; if the exam is asymmetric, or seizures repeat inside 30 days, the next step is imaging under anesthesia, usually 1,500 to 3,000 dollars. Neither check tells you the cause on its own, and no honest answer comes from a video alone.

Telling them apart at 3 a.m.

Pattern	Usual length (seconds)	Events per day that need a call	What the cat is doing
Tremor, both sides	5 to 120	6	awake, eating, stops in sleep
Seizure	30 to 180	2	unconscious, paddles, salivates
Vestibular ataxia	60 to 600	1	awake, head tilt, falls to 1 side
Weakness collapse	10 to 60	2	awake, sinks after 20 steps
Muscle twitch, 1 group	1 to 5	10	awake, skin ripples, no loss

What to do before the appointment

Make the floor survivable: 3 rugs on tile, no stairs after 8 p.m., a litter box with a 10 cm lip, water within 2 metres of the bed, room at 20 to 24 Celsius. Remove diffusers and essential oils, since tea tree, eucalyptus and pennyroyal are all toxic to cats. Keep every medicine in a closed drawer, including non-steroidal painkillers and any diazepam. Feed 4 to 5 small meals rather than 1 large one, and weigh every 3 days, because a 4 kg cat at 3.8 kg is already 5 percent down.

Drugs are prescription only

Phenobarbital, levetiracetam, potassium bromide and zonisamide all need a prescription, a starting dose based on weight and kidney values, and blood monitoring: a phenobarbital level usually kept between 15 and 45 micrograms per ml, with liver enzymes at day 0, day 30 and day 90. Giving a human sedative, an old anticonvulsant from the cupboard, or a supplement sold for calm cats changes the exam findings and can lower the seizure threshold. Ask what is being prescribed, why, and what to watch for in the first 72 hours.

Tracking the pattern over 4 weeks

One line per event, 7 days a week, then a weekly total: number of events, total seconds, and whether food and litter box use were normal that day. Old cats often show a 2 to 3 week drift before a clear change, so 4 weeks is the shortest honest comparison. Bring the sheet and 3 short videos rather than 30; a vet can read 3 clips in 2 minutes and cannot read 30. The weight line on the same sheet is what turns a vague story into a decision, and the weight log shows how to take it.

First 7 days

• Day 1: film 1 baseline clip of the cat standing and walking, even if nothing is happening.
• Day 1: write the toxin list on the fridge and move all medicines into 1 locked drawer.
• Day 2: start the event sheet, 6 fields, 1 line per event, cap at 5 minutes.
• Day 3: put 3 rugs down and move water within 2 metres of the bed.
• Day 4: book 1 visit that covers blood, T4, calcium, potassium and blood pressure.
• Day 7: weigh, and compare with day 0 before deciding to wait another week.

Hydration is the quiet variable here: a trembling cat spills water, drinks less, and dehydrates faster than the shaking suggests. A fountain that runs 24 hours a day keeps intake steady, and the fountain guide covers the cleaning schedule. Total workup cost at most clinics lands between 200 and 500 dollars before imaging, which the cost calculator breaks down by test.

Terms mentioned in this article

T4

Frequently asked

Related guides

• Adopting a Cat With a Tremor: 14-Day Log, 3-Month Checks
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• Senior Cat Not Eating: 24 Hour and 48 Hour Lines
• Senior Cat Won't Eat: The 5-Step Ladder
• Arthritis Screening After 12: 5 Signs to Score
• Senior Cat Cleaning Without a Full Bath