When muscle weakness develops, distinguishing between amyotrophic lateral sclerosis (ALS) and myasthenia gravis (MG) can be difficult — even for doctors. Though these conditions both affect muscle function, their causes, treatments, and outcomes are quite different.

This article will help you understand the relationship between ALS and MG, identify their similarities and differences, and provide you with valuable information to discuss with your healthcare provider so you can better navigate diagnosis and treatment options.

What Are ALS and MG?

Amyotrophic lateral sclerosis is a disease that causes motor neurons — nerve cells in the brain, brain stem, and spinal cord — to break down over time. This leads to progressive muscle weakness and atrophy (muscle loss). Doctors don’t fully understand what causes ALS, which is why there isn’t a cure or highly effective treatments.

Myasthenia gravis, on the other hand, is an autoimmune disease, meaning the body’s defense system mistakenly attacks itself. In MG, the immune system makes antibodies (special proteins) that block the signals between nerves and muscles, making movement more difficult. This leads to muscle weakness and rapid fatigue.

Both ALS and MG are neurological disorders (conditions that affect the nervous system) and impact how muscles function. Having one of these diseases doesn’t necessarily increase your risk of developing the other. In fact, less than 1 percent of individuals with ALS also have MG.

8 Similarities Between ALS and Myasthenia Gravis

Although ALS and MG have different causes, they share several key similarities. Both conditions affect muscle function and can significantly impact daily life.

1. They Can Affect People of Any Age

Both ALS and MG can affect people of any age, but they tend to affect different age groups. ALS is more common in older adults, typically developing after age 50. MG follows a different pattern, according to the Muscular Dystrophy Association, with one peak occurring in younger females (often in their 20s) and another in older males (usually in their 60s to 80s).

2. Muscle Weakness Affects Daily Activities

People with ALS or MG experience muscle weakness that can make routine tasks more difficult. Simple activities like climbing stairs, getting dressed, or preparing meals may become challenging as the conditions progress.

3. They Both Cause Difficulties With Speaking and Swallowing

Dysphagia (difficulty swallowing) and dysarthria (difficulty speaking) are common in both conditions. These symptoms can significantly affect communication and nutrition, making it harder to eat or speak clearly.

4. Breathing Problems May Develop

As ALS and MG progress, they may cause breathing difficulties. Treatments differ, however. In MG, breathing issues often occur during severe flares and may improve with oxygen therapy or a ventilator (breathing machine). In ALS, respiratory decline is permanent, and oxygen therapy alone usually won’t help — or may even be dangerous. A ventilator or noninvasive ventilation is needed to support breathing.

5. Muscle Twitches Frequently Occur

Fasciculations (involuntary muscle twitches) can occur in both disorders, though they are more common in ALS. These twitches can happen anywhere in the body.

6. Fatigue Is a Constant Challenge

Fatigue is a major symptom of both ALS and MG. It’s not just ordinary tiredness but a deep exhaustion that doesn’t improve with rest and significantly affects quality of life.

7. Similar Tests Help Diagnose Both Conditions

Neurologists (doctors who treat diseases of the brain, spinal cord, and nerves) use similar tests to diagnose ALS and MG, including electromyography (EMG), which measures electrical activity in muscles and nerves. These tests can help determine how the nervous system is functioning and differentiate between the two conditions.

8. Neither Condition Has a Cure

There’s no cure for ALS or myasthenia gravis, but treatments are available — especially for MG, where medications can significantly improve symptoms. Research is ongoing to find better treatments and potential cures for both conditions. Regular follow-ups with a neurologist are crucial for managing both disorders and maintaining quality of life.

7 Differences Between ALS and Myasthenia Gravis

Although ALS and MG share some similarities, they are very different diseases. They have distinct causes, symptoms, progression patterns, and treatment approaches. Here’s how they differ.

1. They Have Different Causes

ALS damages motor neurons in the brain and spinal cord, which control movement. Most of the time, doctors don’t know exactly what causes it. Some factors that might add to the risk are:

• Genetic mutations (changes in the genes)
• Environmental toxins
• Immune system abnormalities

Myasthenia gravis, however, is well known as an autoimmune disorder. The immune system mistakenly creates antibodies that attack acetylcholine (ACh) receptors at the neuromuscular junction (NMJ) — the connection point where nerves signal muscles to move. This prevents proper muscle contraction, leading to weakness. Genetic factors can also play a role in MG.

2. They Have Distinct Muscle Weakness Patterns

In ALS, muscle weakness typically begins in the limbs and progresses steadily without improvement. The weakness causes the muscles to waste away, eventually leading to paralysis.

MG muscle weakness often fluctuates. Commonly, it starts with the eye muscles, causing drooping eyelids and double vision. People living with MG also experience weakness in arms, legs, and neck. Unlike ALS, MG doesn't cause muscle atrophy — any muscle loss is likely due to fatigue and lack of muscle use. MG symptoms worsen with activity but improve with rest.

3. Thymus Gland Abnormalities Occur Only in MG

Many people with myasthenia gravis have abnormalities in their thymus gland, including tumors called thymomas. The thymus gland is an organ located behind the breastbone that helps train and develop the immune system, especially during childhood. Since the thymus plays a key role in immune function, its dysfunction may contribute to MG’s autoimmune response.

ALS has no known connection to the thymus gland.

4. Blood Tests Can Help Diagnose MG but Not ALS

Doctors can diagnose myasthenia gravis through blood tests that detect anti-acetylcholine receptor antibodies (proteins in the blood) or muscle-specific kinase (MuSK) antibodies. However, a small percentage of people with MG do not test positive for these antibodies, so additional tests may be needed for diagnosis.

No such blood test exists for ALS. Instead, doctors rely on physical exams, ruling out other conditions, and special nerve and muscle tests.

5. Treatment Approaches Are Different

ALS treatments focus on slowing disease progression and managing symptoms. They include:

• Medications such as riluzole and edaravone to slow disease progression
• Physical therapy and occupational therapy to maintain mobility and improve muscle strength
• Speech therapy to help maintain communication as speaking muscles weaken
• Assistive equipment (wheelchairs, communication aids) to support mobility and speech
• Nutritional support to ensure adequate calorie intake

MG treatments aim to improve muscle function and suppress the immune system. They include:

• Acetylcholinesterase inhibitors, such as pyridostigmine, to improve nerve-muscle signaling
• Immunosuppressants, such as prednisone and azathioprine, to reduce the immune attack
• Complement inhibitors, such as ravulizumab, eculizumab, and zilucoplan, to block immune system overactivity
• Neonatal Fc receptor (FcRn) inhibitors, such as efgartigimod alfa and rozanolixizumab, to remove harmful antibodies
• Plasmapheresis (plasma exchange) or intravenous immunoglobulin for severe symptom flares
• Thymectomy (surgical removal of the thymus gland), which may improve symptoms in some cases

6. ALS Worsens Continually Over Time

ALS symptoms progress steadily and do not improve. Key signs include:

• Progressive muscle weakness (usually starting in the limbs)
• Muscle atrophy and eventual paralysis

For MG, symptoms can fluctuate day-to-day with exacerbations (periods of worsening) and remissions (periods of improvement).

7. Life Expectancy Is Higher in MG

ALS is a progressive disease with no cure. After diagnosis, most people live another three to five years, although some live for 10 years or longer.

With proper treatment, myasthenia gravis typically does not reduce life expectancy. Most people living with MG can lead full lives with managed symptoms.

Talk With Others Who Understand

On MGteam, the social network for people living with myasthenia gravis and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Do you know someone living with myasthenia gravis or ALS? Share your experience in the comments below, start a conversation by posting on your Activities page, or connect with like-minded members in Groups.