Conditions like myasthenia gravis, multiple sclerosis, and other motor neuron diseases can mimic ALS due to similar symptoms. Doctors may need several tests to rule out other conditions.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the progressive loss of motor neurons in the brain and spinal cord, leading to muscle weakness and atrophy.

However, several diseases mimic ALS due to overlapping symptoms, making an accurate diagnosis challenging. It can take more than a year to arrive at an accurate ALS diagnosis.

Read on to learn more about diseases that mimic ALS, including how doctors distinguish between them and ALS.

Symptoms of ALS

Common ALS symptoms include:

  • muscle weakness
  • muscle atrophy
  • twitching
  • muscle stiffness
  • difficulty swallowing (dysphagia)
  • difficulty speaking (dysarthria)
  • breathing problems
  • fatigue
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Myasthenia gravis (MG) is a neuromuscular disorder that can mimic ALS due to shared symptoms like muscle weakness. However, there are distinct differences.

MG typically features fluctuating muscle weakness that worsens with use, often starting in the eye muscles.

Doctors distinguish MG from ALS through specialized tests like repetitive nerve stimulation, which reveals a characteristic decrement in muscle response. Blood tests can also detect acetylcholine receptor or muscle-specific kinase antibodies indicating MG.

Unlike ALS, which is progressively debilitating with no cure, MG has effective treatments like acetylcholinesterase inhibitors or immunosuppressive medications.

Multiple sclerosis (MS) is another neurological condition that can sometimes be mistaken for ALS due to overlapping symptoms. It typically presents with episodes of neurological dysfunction that come and go (relapsing-remitting), while ALS involves progressive, steady motor neuron degeneration.

Diagnostic tools like MRI can reveal characteristic MS lesions in the central nervous system, helping to distinguish between the two conditions. Specific blood tests and cerebrospinal fluid analysis can also help a doctor distinguish MS from ALS.

Unlike ALS, MS has disease-modifying therapies to manage symptoms and slow its progression.

Several motor neuron disorders mimic ALS, including:

  • Primary lateral sclerosis (PLS): PLS is a rare motor neuron disorder characterized by progressive weakness, stiffness, and spasticity in the limbs. But unlike ALS, PLS primarily affects your upper motor neurons.
  • Progressive muscular atrophy (PMA): PMA affects your lower motor neurons, resulting in muscle weakness and wasting. This is similar to ALS but without the upper motor neuron involvement often seen in ALS.
  • Hereditary spastic paraplegia (HSP): This group of genetic disorders causes spasticity and weakness, often starting in the lower limbs. While it shares spasticity with ALS, it doesn’t involve motor neuron degeneration.
  • Kennedy’s disease: This rare genetic disorder primarily affects the bulbar and spinal regions, causing muscle weakness and atrophy. It can resemble ALS but has distinct genetic markers. It’s an X-linked condition, meaning it affects mostly males.
  • Multifocal motor neuropathy (MMN): MMN can mimic ALS with muscle weakness, but it typically presents asymmetrical symptoms and responds well to intravenous immunoglobulin therapy.

Infections like Lyme disease and HIV can present symptoms that mimic ALS.

Lyme disease can lead to neurological symptoms such as muscle weakness and spasticity. Distinguishing it from ALS involves a detailed medical history and blood tests for Lyme antibodies.

HIV-associated neurological complications, including motor dysfunction, can also mimic ALS. Differentiating between the two depends on HIV testing and other HIV-related symptoms.

Hyperthyroidism can mimic ALS symptoms due to muscle weakness, tremors, and weight loss. Doctors can use thyroid function tests to reveal elevated thyroid hormone levels to differentiate hyperthyroidism from ALS.

Effective treatment for hyperthyroidism, such as antithyroid medications or radioactive iodine, can resolve symptoms.

Vitamin B12 deficiency can cause neurological symptoms resembling ALS, including muscle weakness and numbness. Blood tests revealing low B12 levels confirm the deficiency.

Vitamin B12 supplementation can reverse these symptoms, distinguishing it from the irreversible progression of ALS.

Post-polio syndrome can mimic ALS, leading to muscle weakness and fatigue. A history of prior polio infection and electromyography (EMG) findings help differentiate it from ALS.

Unlike ALS, the weakness in post-polio syndrome is generally stable, and management involves rehabilitation strategies to improve function.

Spinal cord compression (myelopathy) or a pinched nerve (radiculopathy), particularly in the neck or lower back, can also cause symptoms similar to ALS. They can also present similar findings on certain diagnostic tests, like EMG.

In addition to motor symptoms, radiculopathy also causes sensory loss and neuropathic pain — symptoms not commonly seen in ALS. Also, in contrast to ALS, myelopathy can cause severe neck pain and loss of control of your anal sphincter.

Doctors use a combination of clinical evaluations to assess your medical history and symptoms, looking for signs characteristic of ALS. They can also use diagnostic tests to either confirm or rule out ALS, including:

  • EMG and nerve conduction studies: These tests measure electrical activity in muscles and nerves. In ALS, EMG often shows signs of muscle denervation and twitching.
  • MRI and CT scans: Imaging studies can help doctors rule out other diseases that mimic ALS. While they can’t confirm ALS, they can indicate muscle atrophy or structural abnormalities.
  • Blood tests: Doctors use blood tests to rule out conditions with similar symptoms, such as thyroid disorders or infections. ALS itself doesn’t have specific blood markers.
  • Genetic testing: A doctor may recommend genetic testing to identify known ALS-associated genetic mutations in familial cases.

Here are some frequently asked questions about diseases that mimic ALS.

How often is ALS misdiagnosed?

ALS is initially misdiagnosed in about 10% of cases, often due to its similarity to other conditions.

How long does it take to diagnose ALS?

Diagnosing ALS can take several months, with an average of 10–16 months from symptom onset to confirmation.

What is the tongue test for ALS?

The tongue test is not a formal diagnostic test for ALS. Doctors assess tongue weakness as part of the clinical examination to evaluate motor neuron dysfunction.

Tongue fasciculation (twitching) may be an early sign of ALS. But ALS isn’t the only cause of tongue fasciculation.

Several disorders share similar symptoms with ALS, such as muscle weakness, twitching, and atrophy. Common mimics of ALs include MG, MS, and other motor neuron diseases.

Doctors use a combination of clinical evaluation, specialized tests, and exclusion criteria to distinguish ALS from diseases that mimic it. Seeing a doctor early about concerning symptoms can help start the often lengthy diagnostic process sooner.