What Is the Difference Between Kennedy's Disease and ALS?

Medically Reviewed on 12/30/2022
Kennedy's Disease vs ALS
Although they share symptoms, Kennedy’s disease is different than amyotrophic lateral sclerosis (ALS).

Kennedy's disease is a type of motor neuron disease that may clinically mimic amyotrophic lateral sclerosis (ALS). However, unlike Kennedy's disease, ALS does not have endocrine disorders of loss of sensation.

As ALS involves degeneration of upper motor neurons, the person has increased reflexes and abnormal stiffness of muscles (spasticity), reducing muscle movements. These are not seen with Kennedy's disease.

The diagnosis of Kennedy's disease can be made based on clinical signs and electrodiagnostic testing such as electromyography or nerve conduction studies that measure the electrical activity of muscles and nerves. Confirmation needs a simple blood test that looks for the faulty gene in the DNA.

What is Kennedy’s disease?

Kennedy's disease, also known as spinal and bulbar muscular atrophy, is a rare, X-linked recessively inherited disease as the affected AR gene is located on the X-chromosome. This neurodegenerative condition affects lower motor neurons. It is estimated that 1 in 40,000 men is affected. It is extremely rare in women, but all women with this gene are carriers. 

Kennedy's disease is an adult-onset disorder, with illness onset ranging from 30 to 50 years with a normal life expectancy. The progression of Kennedy's disease is relatively slow compared with that of other motor neuron diseases such as amyotrophic lateral sclerosis (ALS). 

Kennedy's disease mostly affects men and is characterized by muscular weakness and atrophy, commonly accompanied by additional signs and symptoms such as gynecomastia, impotence, testicular shrinkage, and metabolic abnormalities, indicating multisystem involvement.

The most common symptoms of Kennedy's disease include tremors in the limbs and muscle spasms. Muscular weakness in the legs makes walking difficult and increases the risk of falls. As bulbar muscles (muscles of the head and neck) are involved, difficulties with swallowing and speech develop gradually.

What is ALS?

Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig’s disease, is an idiopathic (cause is unknown), deadly progressive neurodegenerative disease of the motor system (nerves that control muscles) including both upper motor neurons (brain) and lower motor neurons (spinal cord). 

Motor neurons regulate voluntary muscles, and as these motor neurons die, the muscles they control become weak and eventually become nonfunctional, resulting in muscular weakness, paralysis, and death. 

Researchers believe that certain people are genetically prone to getting the condition but only after coming into touch with an environmental trigger. The combination of heredity and environment may explain why some people get ALS.

Although most ALS cases are spontaneous, which means there is no family history of the disease, about 10 percent of cases are familial, which means the disease runs in the family. 

  • Most people with ALS die within three to five years of being diagnosed.
  • About 30 percent of patients with ALS survive 5 years following diagnosis, and 10 to 20 percent survive 10 years or longer.
  • Some people may survive beyond the age of 20 years, but it is rare.
  • Men and young people have higher survival rates.


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How causes Kennedy’s disease?

Kennedy’s disease is caused by a mutation in the AR gene, which codes for the AR protein. This protein is distributed throughout the body; however, high concentrations in motor neurons regulate voluntary muscles.

The gene mutation results in the production of an abnormally big protein with an altered structure. The exact mechanism of nerve cell destruction leading to Kennedy's disease is unknown. However, it is believed that the abnormal protein would accumulate within the cells until it disrupts their normal function and triggers their death.

Common misdiagnosis

Amyotrophic lateral sclerosis has been the most common misdiagnosis. Other disorders that have symptoms similar to those of Kennedy's Disease and have led patients to be misdiagnosed include:

Medically Reviewed on 12/30/2022
Image Source: iStock image

Kennedy's Disease: https://www.aanem.org/Patients/Muscle-and-Nerve-Disorders/Kennedys-Disease#:~:text=A%20key%20feature%20that%20distinguishes,reflexes%20and%20spasticity%20in%20ALS.

Kennedy Disease: https://www.sciencedirect.com/topics/nursing-and-health-professions/kennedy-disease