Is my thigh tremor a sign of ALS or Prozac side effects?

Hello,

Welcome to icliniq.com.

I have gone through your query and understand your concern.

Based on what you shared, a normal neurological exam, normal EMG (electromyography, a diagnostic procedure that evaluates the health of muscles and the nerve cells that control them), and normal blood work make ALS (amyotrophic lateral sclerosis, or Lou Gehrig's disease, a progressive, terminal neurodegenerative disease) very unlikely.

In ALS, the key problem is progressive true weakness (dropping things, foot drop, trouble standing from a chair), and the exam and EMG usually show clear evidence of ongoing nerve–muscle damage. Muscle twitches (fasciculations) by themselves are common and often benign, especially when strength and EMG are normal.

The internal vibration or tremor-like feeling in a localized area (right quadriceps), especially during movement, is commonly caused by muscle overuse, local muscle irritability, anxiety or an adrenaline surge, dehydration, poor sleep, excess caffeine, or after exercise or strain. Many people describe it as a buzzing feeling inside the muscle. This pattern fits much more with benign fasciculation syndrome or anxiety-related body sensations than ALS.

Prozac (Fluoxetine) can absolutely contribute. Even at 10 mg, early side effects in the first days to a few weeks can include jitteriness, inner restlessness, tremor or shakiness, muscle twitching, increased awareness of body sensations, and anxiety activation. This is sometimes called activation and often improves as your body adapts (commonly over one to three weeks, sometimes a bit longer). So, the timing you mention makes Prozac a very plausible contributor to the internal vibration or tremor sensation.

You should adopt simple, practical steps, including reducing stimulants (coffee or energy drinks), hydrating well, ensuring good sleep, adding gentle quad stretching, and avoiding heavy leg workouts for a few days.

Many patients also benefit from checking and correcting common contributors to twitching or tremor, such as magnesium, vitamin D, vitamin B12, thyroid (TSH or thyroid-stimulating hormone), and calcium or potassium, if not already checked, not because ALS is suspected, but because these can worsen twitching and internal tremor symptoms.

Please seek urgent review if you develop new, clearly progressive weakness (knee buckling, cannot climb stairs like before), visible muscle wasting, speech or swallowing trouble, or if you have fever, severe rigidity, confusion, heavy sweating, diarrhea, or fast heartbeat after medication changes (these are uncommon but important medication-related warning signs).

Otherwise, with your normal exam and EMG, the best next step is usually a follow-up with the prescribing doctor to discuss whether to continue and observe, slow titration, or consider an alternative if the symptoms are very uncomfortable.

I hope I have answered your question.

Let me know if I can assist you further.

Thank you.

Hello doctor,

Welcome back to icliniq.com.

I have gone through your query and understand your concern.

Internal tremor or internal vibration is not how ALS (amyotrophic lateral sclerosis) typically presents. ALS damages the motor nerves that control muscles. The first symptom is almost always progressive weakness, not a vibration feeling.

Patients usually notice they cannot do something they could previously do, like lifting the foot properly, gripping tightly, climbing stairs, or raising an arm. An internal buzzing sensation alone is not characteristic of ALS.

The fact that you ran two miles is very reassuring. In ALS, muscles become progressively weak and fatigue easily because the nerve supply is failing. If you are able to run two miles with normal coordination and no true weakness, that strongly argues against ALS. ALS does not hide during activity; weakness shows itself.

Also, you mentioned your neurological exam and EMG (electromyography) were normal. A normal EMG in the setting of symptoms like this is a very strong reassurance. ALS would almost always show abnormalities on EMG when symptoms are present.

Internal tremor, especially after starting Prozac (Fluoxetine), along with anxiety about health, fits much more with nervous system sensitivity and medication activation effects, not a degenerative motor neuron disease. From a neurological standpoint, your ability to exercise normally and maintain strength is one of the strongest reassuring signs.

I hope I have answered your question.

Let me know if I can assist you further.

Thank you.

Hello,

Welcome back to icliniq.com.

I have gone through your query and understand your concern.

Even though the internal vibration started after your EMG (electromyography) and MRI (magnetic resonance imaging), that does not change the reassurance those tests provide.

A normal neurological exam, normal EMG, and normal MRI together make ALS (amyotrophic lateral sclerosis) extraordinarily unlikely. ALS does not suddenly appear days or weeks after a completely normal evaluation and present only as a vibration feeling.

Now about Prozac (Fluoxetine). It is not unheard of at all for SSRI (selective serotonin reuptake inhibitors) activation effects to feel localized. The medication affects the central nervous system, increasing nerve excitability slightly in the early phase. But how that sensation is perceived can be very focal. Many patients report:

1. One eyelid twitch.

2. One calf is vibrating.

3. One thigh is buzzing.

4. One hand is shaky.

The brain can amplify sensations in one body part, especially when anxiety is high, and attention is focused there. The muscle itself is not diseased; it is just temporarily more irritable or more noticeable.

If this were ALS, you would not be describing:

1. A vibration only during movement.

2. No weakness.

3. Ability to run two miles.

4. Normal exam.

5. Normal EMG.

6. Normal MRI

ALS causes failure of strength, not isolated sensory-like vibration feelings. It does not produce an internal shaking sensation as a first or isolated symptom.

What I am hearing very clearly is an OCD (obsessive compulsive disorder is a chronic mental health condition) reassurance loop:New sensation leads to the thought, Is this ALS?, which triggers an anxiety spike. The anxiety then amplifies normal body sensations, leading to more checking and monitoring, which increases fear and reinforces the cycle.

That cycle is extremely common in health anxiety and OCD, and ironically, SSRIs can temporarily increase body awareness in the first couple of weeks before helping long-term.

It would not be unusual for Prozac or anxiety activation to make one feel this way. Being able to run two miles is a very strong reassurance. This pattern is not how ALS presents.

Right now, the bigger issue is the anxiety loop, not a neurological disease. And the fact that you are seeking treatment for OCD is actually the healthiest sign in this whole conversation.

I hope I have answered your question.

Let me know if I can assist you further.

Thank you.