Does ALS Cause Tremors? A Look at the Symptoms

ALS, or amyotrophic lateral sclerosis, is not a tremor-producing disease. The hallmark symptoms are progressive muscle weakness, wasting, and stiffness, not the rhythmic shaking most people picture when they hear the word “tremor.” That said, the relationship between ALS and involuntary movements is more tangled than a simple no. Fasciculations, jaw clonus, and even a mechanical form of action tremor have all been documented in people with the disease, and a rare overlap syndrome can produce classic Parkinsonian tremor alongside ALS.

What ALS Actually Does to the Body

ALS attacks motor neurons, the nerve cells responsible for voluntary muscle movement. As those neurons degenerate, muscles lose their nerve supply, weaken, and eventually waste away. The disease hits both upper motor neurons (in the brain and spinal cord) and lower motor neurons (connecting the spinal cord to the muscles), which is what sets it apart from conditions that only affect one or the other.

The symptoms people experience depend on which motor neurons are affected first and how quickly the disease progresses. Early signs often include tripping, dropping things, difficulty buttoning a shirt, or slurred speech. Stiffness and muscle cramps are common. But the defining feature is weakness that gets steadily worse over time, spreading from one region of the body to others. This is fundamentally different from tremor diseases, which involve involuntary rhythmic movement but not the relentless loss of strength and muscle bulk that characterizes ALS.

Fasciculations Are Not Tremors

The symptom most often mistaken for tremor in ALS is the fasciculation, a brief, involuntary twitch visible under the skin. Fasciculations look like a small flicker or ripple in a muscle, sometimes described as a worm moving beneath the surface. They are spontaneous, irregular, and usually painless. In ALS, they arise because damaged lower motor neurons become electrically unstable, firing off signals on their own.

A tremor, by contrast, is a rhythmic, oscillating movement of a body part. Think of the steady shaking of a hand at rest in Parkinson’s disease or the wobble of a hand held outstretched in essential tremor. Fasciculations have no rhythm. They fire in unpredictable bursts, affect tiny portions of a muscle rather than moving an entire limb, and do not produce the kind of visible shaking that a tremor does.

The confusion between the two is understandable. Both are involuntary, both involve muscle activity the person did not initiate, and both can alarm anyone who notices them. But physiologically they are distinct events. Fasciculations originate from individual motor units firing spontaneously, whereas tremors involve coordinated, alternating contractions of opposing muscle groups. Fasciculations in ALS fire at a higher rate and appear more widely across the body compared to the benign fasciculations that healthy people experience, which are common enough that most adults have felt a twitching eyelid or calf muscle at some point.

Research comparing fasciculations in ALS to benign fasciculations found that the waveforms are not reliably distinguishable on shape alone. What does differ is the firing rate, which is significantly higher in ALS, along with a greater frequency of “double fasciculations,” pairs of twitches firing in rapid succession, especially when lower motor neuron damage is pronounced.¹ Crucially, fasciculations are not unique to ALS. They occur in many other conditions and in perfectly healthy people, a point that deserves emphasis because many people who notice muscle twitching immediately fear ALS.²

Why Fasciculations Rise and Then Fall in ALS

There is a pattern to fasciculations across the course of ALS that can confuse both patients and clinicians. Early in the disease, when muscles are still relatively strong, fasciculations tend to increase. This happens because the motor neurons that are becoming diseased grow hyperexcitable before they die. Sodium and potassium channels in those nerve membranes stop working properly, making the neurons more likely to fire on their own.

As the disease progresses and more motor neurons die off entirely, the pool of neurons available to twitch shrinks. So fasciculations eventually decline, not because anything is getting better, but because fewer motor units remain. Studies tracking fasciculation frequency over time in ALS patients have confirmed this rise-and-fall trajectory, observing that fasciculations peak while muscles still have reasonable strength and then taper off as weakness becomes severe.³ For someone watching a loved one with ALS, the fading of visible twitches may seem reassuring, but it actually reflects advancing disease.

Tremor-Like Movements That Do Appear in ALS

While classical tremor is not part of ALS, there are at least two involuntary movements in ALS patients that can look remarkably tremor-like to a non-specialist.

The first is jaw clonus. Clonus refers to involuntary, rhythmic contractions triggered by a hyperactive stretch reflex. In ALS, damage to upper motor neurons can make the trigeminal nerve reflex that controls jaw muscles overactive, producing rapid, rhythmic jaw movements. These movements look like tremor and can easily be mistaken for one, but they have a different mechanism: they are driven by a reflex loop rather than the central oscillator circuits that produce true tremors. One report analyzing the frequency of rhythmic jaw movements in an ALS patient found a peak around 10 Hz, faster than what is typical in Parkinson’s tremor, essential tremor, or other jaw-movement disorders.⁴ Clinicians note that jaw clonus can be distinguished from tremor by examining whether it is triggered by a stretch of the jaw muscles, though when it occurs spontaneously the distinction becomes harder to make.⁵

The second is action tremor. A study examining hand tremor in motor neuron disease patients found that many did in fact have shaky hands during movement. Using accelerometers, researchers determined that the tremor frequency decreased when weight was added to the hand, a hallmark of mechanical-reflex tremor.⁶ This means the shaking is not generated by a brain circuit gone haywire, as in Parkinson’s or essential tremor. Instead, it appears to result from weakened muscles struggling to maintain a steady posture or complete a controlled movement. When muscles have lost some of their motor units, the remaining ones fire less smoothly, producing visible shakiness. This is a tremor in the everyday sense of the word, but it is a downstream effect of weakness rather than a primary feature of the disease.

When ALS and Parkinson’s Disease Overlap

There is a rare but real condition in which a person genuinely has both ALS and Parkinson’s disease simultaneously. Known as Brait-Fahn-Schwartz disease, it was first described decades ago and has been documented in scattered case reports since. In these patients, you see the typical ALS picture of progressive weakness, wasting, and upper motor neuron signs, alongside classic Parkinsonian symptoms including resting tremor, slowness of movement, and rigidity. Clinical evidence for some degree of parkinsonism may accompany ALS in roughly 5 to 17 percent of cases, though the full-blown combination remains rare.⁷

In one case, a 55-year-old man presented with slowing of his movements followed by resting tremor in his right hand, and then progressed to weakness in all four limbs.⁸ A case series examining overlap syndromes between parkinsonism and motor neuron disease identified seven patients with ALS-parkinsonism (Brait-Fahn disease) and four patients who also had frontotemporal dementia layered on top.⁹ In Brait-Fahn-Schwartz disease, the parkinsonism tends to respond to levodopa, the standard Parkinson’s medication, which underlines that the tremor in these patients is coming from the Parkinson’s component, not from the ALS itself.

This overlap matters for two reasons. First, if someone with an ALS diagnosis develops resting tremor, it should prompt consideration of whether a concurrent Parkinsonian process is at work. Second, the tremor in these cases is treatable even when the underlying ALS is not, which can meaningfully improve quality of life.

Conditions That Mimic ALS and Involve Tremor

Part of the anxiety around ALS and tremor comes from the diagnostic process itself. ALS is diagnosed mainly by ruling out other conditions, and several of those look-alikes do feature prominent tremor. If you are experiencing both weakness and tremor, the differential diagnosis matters enormously, because some of these alternatives are treatable or much slower-progressing.

Kennedy’s disease (X-linked spinal and bulbar muscular atrophy) is one of the most important ALS mimics. It is a genetic motor neuron disease that affects men, causing progressive weakness, muscle wasting, and fasciculations, much like ALS. But unlike ALS, Kennedy’s disease progresses much more slowly and has a distinctive feature: tremor is present in a large majority of patients. One study found postural hand tremor in 80 percent of Kennedy’s disease patients.¹⁰ If someone has the combination of slowly progressive weakness, fasciculations, and a prominent hand tremor, Kennedy’s disease is a diagnosis worth pursuing, because the prognosis is far better than ALS.

Multifocal motor neuropathy (MMN) is another condition that can be confused with ALS. It causes weakness and can produce fasciculations, but it affects only the lower motor neurons and tends to stay in the distribution of individual nerves rather than spreading diffusely. One distinguishing feature is that fasciculations in MMN tend to be less widespread: researchers found that fasciculation detection rates on the affected side were significantly lower in MMN compared to ALS, and crucially, MMN patients had no fasciculations in the tongue or trunk, areas commonly involved in ALS.¹¹ MMN matters because it responds to immunoglobulin treatment, a therapy that does nothing for ALS.¹²

Why the Distinction Between Fasciculations and Tremor Matters for Diagnosis

For the person sitting in a neurologist’s office worried about twitching or shaking, the distinction between fasciculation and tremor is more than academic. Fasciculations without weakness are overwhelmingly benign. The vast majority of people who experience isolated muscle twitching, even persistent, widespread twitching, do not have ALS. Benign fasciculation syndrome is far more common and, while annoying, is not dangerous.

The studies that have investigated where fasciculations originate found that the site of origin differs between conditions. In benign fasciculation syndrome, a larger proportion of fasciculations originate at the spinal cord level, while in ALS, particularly in muscles that have undergone reinnervation (where surviving motor neurons have taken over for lost ones), more fasciculations originate distally along the nerve itself.¹³ This is an important technical point for neurologists doing electrodiagnostic testing, but for the patient it translates to something simpler: twitching alone is not an ALS diagnosis. The clinical context, including whether there is progressive weakness, muscle wasting, and changes in reflexes, determines whether fasciculations are worrisome.

Tremor, on the other hand, should steer the diagnostic conversation away from ALS entirely in most cases. Resting tremor suggests Parkinson’s disease or a related movement disorder. Postural and action tremor point toward essential tremor, enhanced physiological tremor, or conditions like Kennedy’s disease. If both tremor and ALS-like weakness are present, that is when the rarer overlap syndromes and mimics deserve careful investigation.

Managing Jaw Clonus and Spasticity in ALS

For ALS patients who do develop rhythmic involuntary movements, particularly jaw clonus, management focuses on reducing spasticity. Jaw clonus is more than a curiosity: it can interfere with eating, speaking, and cause pain. Standard anti-spasticity medications like baclofen and tizanidine are often used, though the doses needed to control jaw clonus tend to be high enough that side effects such as sedation and increased weakness become limiting. Benzodiazepines carry the additional problems of tolerance and dependence. Dextromethorphan-quinidine, a drug approved for pseudobulbar affect (the uncontrollable laughing or crying episodes that occur in some ALS patients), has been tried off-label for jaw clonus and other bulbar symptoms, with emerging case reports suggesting some benefit.⁴

The action tremor caused by weakened muscles is harder to treat directly, because the underlying issue is loss of motor neurons rather than a correctable imbalance. Physical and occupational therapy can help patients adapt, and assistive devices like weighted utensils or wrist supports can sometimes dampen the shakiness enough to maintain function for longer. None of these approaches stop the disease’s progression, but they can make daily life more manageable during the period when the tremor is most noticeable.

Imaging and Nerve Testing in the Diagnostic Workup

Part of the process of ruling in or ruling out ALS involves nerve conduction studies, electromyography, and sometimes MRI of peripheral nerves. In both ALS and MMN, MRI abnormalities of peripheral nerves are surprisingly common, appearing in roughly 58 percent of ALS patients and 63 percent of MMN patients in one study, with most changes being mild to moderate.¹⁴ The overlap in imaging findings between these conditions illustrates why no single test clinches the ALS diagnosis. Clinicians rely on the overall pattern: the combination of upper and lower motor neuron signs, progressive spread across body regions, and the absence of features that point to something else.

For someone experiencing tremor alongside weakness, the diagnostic workup typically includes blood tests (to check for Kennedy’s disease and other genetic conditions), nerve conduction studies (to look for the conduction block characteristic of MMN), and possibly brain imaging (to evaluate for Parkinson’s disease or structural lesions). The goal is not just to confirm or deny ALS, but to identify any treatable condition that might be causing the symptoms.