Doctor reveals cause of Celine Dion's on-camera spasm after singer gives inside look into her struggle with extremely rare stiff person syndrome

The debilitating stiff person syndrome suffered by Celine Dion and one in a million people causes muscle spasms so powerful they can break bones.

A newly-released clip from Celine Dion’s biographical documentary showed the Canadian singer stiff as a board and wailing in pain as muscle spasms overtook her body.

Doctors say the rare condition is caused by a turbocharged immune system reaction that attacks the body’s own cells - specifically, those that regulate motor function.

One doctor told DailyMail.com that with stiff person syndrome (SPS), it is 'as if the body's “off switch” for muscle contraction is malfunctioning, leaving muscles in a constant state of activation.’

In her documentary, Celine Dion suffers a severe, painful full-body spasm that leaves her unable to move a muscle

In the documentary, Ms Dion is performing physical therapy exercises when the spasms overcome her and she has to lay down stationary on her side.

Her wrist is stiff and bent, and she cannot move it. Her face is contorted in pain and she’s crying but she can’t move her neck or head.

Dr James Chung, an expert in autoimmune diseases and Chief Medical Officer at Kyverna Therapeutics, told DailyMail.com: ‘Patients with [stiff person syndrome] often describe their pain as intense sharp pain that makes it hurt to move. Many report a constant underlying muscle tension as if their body is perpetually braced.

‘During acute spasms, patients have likened the sensation to severe cramping or their muscles being "locked" in place. Some describe a burning or electrical sensation accompanying the spasms.’

Dr James Chung [pictured] explained in SPS, the body's own immune system inhibits production of a neurotransmitter that regulates muscle movements and contractions

Her legs also appear completely immobilized out in front of her.

During her crisis, Ms Dion’s doctor administers a benzodiazepine spray to relieve anxiety and reduce muscle spasms.

Her spasms last at least 30 minutes before she’s able to sit up on her own.

Ms Dion says in the aftermath: ‘Every time something like this happens, it makes me feel so embarrassed.

‘I don't know how to express it, you know, to not have control over yourself.’

SPS is an attack on one’s own body, specifically the central nervous system (CNS). SPS produces antibodies that attack proteins responsible for regulating muscle contractions.

This attack reduces levels of an enzyme that produces a major CNS neurotransmitter called GABA, which usually relaxes the muscles. But when its levels are reduced, the muscles don’t receive signals to release tension, leading to prolonged muscle contraction. 

Outside stimuli, such as bright lights or loud noises, often bring on spasms, and emotional distress can prompt or worsen the involuntary movements. 

Dr Chung said: 'This autoimmune attack leads to muscles now not having proper control over how they contract and relax, leading to stiffness, reduced movement, excessive muscle tension and painful spasms.'

Celine Dion dealt with stiff person syndrome secretly for 17 years before going public with her diagnosis in 2022. The condition makes performing extremely difficult but she is eager to get back to her music career

Spasms can last seconds up to an hour and have been described by sufferers such as San Diego-based Carrie Jean Robinette as causing ‘excruciating pain’ that leaves her ‘temporarily paralyzed’ and ‘feeling like I’ve been physically beaten.’

She said: ‘Every day, I face this condition that looks different, sometimes by the hour.

‘Some days I walk unassisted, others I need my forearm crutch, and most days I need a mobility chair if I’m going to walk more than 20 yards.’

SPS is exceedingly rare, affecting fewer than 5,000 Americans.

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The disease is chronic and cannot be cured. SPS itself isn't fatal, but patients can die from complications of the disease.

Muscle spasms and stiffness compound the risk of deadly falls and injuries. 

Muscle rigidity can also apply to muscles in the chest and diaphragm, leading to breathing failure.

Some people may also experience problems with their autonomic nervous system — the network of nerves that regulates functions we don’t think about, including heart rate, blood pressure, and digestive function.

Treating the condition typically involves muscle relaxants such as diazepam and immunotherapy to reduce the amount of antibody attacks on the body. 

Pain management is crucial but may not necessarily be provided with an opioid, which can be addictive.

Physical therapy, such as the type Ms Dion does, is also essential to maintaining mobility and muscle strength over time.