"Fasciculation" is a mouthful, but it's pretty simple in meaning: a minor contraction of muscles in a specific area. If you notice Mittens twitching, pay attention to the context. She may be excited or agitated about what's happening right then, or a medical reason may be behind the movement.
Twitches and Tremors
A twitch isn't a medical condition; on its own, it's harmless. Twitches and tremors, formally known as fasciculations, are involuntary muscle movements alternating between contraction and relaxation. They can be rapid or slow and can occur anywhere in Mitten's body; some are localized and some go throughout the body. Tremors concentrated in one area tend to occur in the head or hind legs. Fasciculations usually have harmless causes, though sometimes more serious conditions are behind the tremors.
If Mittens has a window seat where she can engage in some birdwatching, you've probably noticed her tail twitching in excitement. Rapid tail movement is a sign she's excited or agitated about something. If she's sprawled out in her favorite chair, enjoying one of her numerous daily naps, don't be surprised if she has a tremor or two. It's perfectly normal for cats to twitch during the rapid-eye-movement phase of their sleep.
Some fasciculations have fairly straightforward causes. If Mittens has itchy skin, she'll twitch in response in the affected area; ear mites cause similar twitching, as the little critters irritate her ears. Life changes, such as a new family member or living quarters, can cause anxiety, potentially leading to tremors. More serious medical causes for twitches include low blood calcium levels, hypoglycemia, vitamin B1 deficiency, magnesium deficiency, kidney disease, rabies and poisoning from medication, plants or other toxic substances. Tremors can also accompany seizures and trauma. Feline hyperesthesia, known as rolling skin disease, can also cause twitching, among other symptoms.
Treating the Twitch
If Mittens is twitching in her sleep, there's no reason for concern. If she's twitching regularly for no apparent reason, take her to the vet, particularly if she shows other symptoms. Her medical history, symptoms and location of the fasciculations will be considered, along with lab work including a complete blood count, urinalysis and biochemistry profile. Occasionally X-rays, CT-scans or MRIs may be required. The goal of treatment is to determine the underlying cause of the tremors. Treatment can include vitamin or mineral supplementation, prescribing an anti-inflammatory, antibiotic or anti-parasitic medication, inducing vomiting if poisoning is suspected, or changing medication. Sometimes the cause of the twitching is idiopathic, or unknown; if that's the case with Mittens, the vet may prescribe medication to help control her twitching.