She had a voice described as a “grand mansion of sound”, won four Grammy awards and thrilled audiences in the world’s opera house – but suddenly stopped performing in 2015.

When Jessye Norman died four years later at the age of 74, her family said she had passed away from septic shock and multi-organ failure secondary to complications of a spinal cord injury she had sustained in 2015. The circumstances surrounding the injury and disappearance from public life were never explained.

However, it can be revealed that Norman’s brother is suing two renowned doctors and a leading London private hospital for allegedly leaving her paralysed when she underwent surgery in 2015 to try and cure a longstanding and painful back problem.

James Howard Norman Sr has launched a lawsuit alleging that medical negligence by anaesthetist and pain specialist Dr Adnan Al-Kaisy, consultant spinal surgeon Khai Lam and the London Bridge hospital left his sister unable to move her body below the waist.

The doctors and hospital are disputing his claims.

The singer’s brother alleges that she suffered horrendous damage as a result of undergoing a procedure called epidurolysis, which is used to dissolve scar tissue around nerves in the spine.

His claim, which has been lodged at the high court in London, alleges that a series of mistakes meant “the deceased was effectively paralysed from the waist downwards, she could not walk, she could not stand even in a standing frame and she was wheelchair-bound”.

It continues: “She needed extensive care. She lived out her days in a rented apartment in New York since she could not access her home in Westchester County.”

The document claims that Al-Kaisy performed the epidurolysis despite the “limited evidence of the procedure’s efficacy, and little if any evidence of its safety”, despite the operation being little-used in the UK and the fact that it was not recommended by the National Institute of Health and Care Excellence (Nice) for back pain. It also accuses the doctor of not warning the singer of these weaknesses and not acquiring her informed consent to proceed with the procedure in those circumstances.

Norman’s brother contends that Lam also failed to warn the star about the limitations of the epidurolysis and that the procedure was the wrong treatment for the condition she was suffering from, called spinal stenosis. He claims Lam did not warn his sister “of the significant risk of paralysis arising from the procedure, in particular severe and permanent damage to the nerves involving paralysis and loss of the use of the lower part of the body”.

According to Norman his sister developed sciatica in March 2015 after undergoing surgery in New York the month before. A week later she came to London to fulfil some engagements and, on the advice of one of her doctors in her native United States, had a consultation with Lam at the London Bridge hospital. He noted that standing for a few minutes left her with pain and numbness in her right leg. He tried two treatments – steroid injections and inserting a “distraction device” – but neither relieved her symptoms.

Norman Sr’s claim says that Lam then suggested that the singer undergo epidurolysis, and suggested that Al-Kaisy could perform it. Both undertake private medical treatment and also work at Guy’s and St Thomas’ (GSTT), the leading NHS trust in London. Al-Kaisy performed the procedure at the London Bridge private hospital on 12 May 2015.

Both doctors are leading practitioners in their areas of medical expertise. Lam has regularly had articles published in medical journals and spoken at many medical conferences. The website for the GSTT’s private patient unit says that Al-Kaisy “has an international reputation as a leading expert in pain management”.

The legendary soprano was still in hospital in London after her treatment in 2015 when she first sought advice from law firm Leigh Day about taking legal action, and formally launched proceedings the next year. Her brother took over as the claimant when she died in 2019.

His claim also alleges that HCA, the giant American healthcare firm which owns and runs the London Bridge hospital, was negligent in not ensuring that the epidurolysis Lam and Al-Kaisy had recommended was safe, appropriate and evidence-based.

Olive Lewin, the specialist medical negligence solicitor at Leigh Day who is representing Norman Sr in the action, said: “The injuries Miss Norman sustained made her final years extremely difficult. It is a sad fact that despite wanting to, she was unable to continue engaging in the activities and events she loved most in the last four years of her life.

“Jessye Norman had painful sciatica, and was admitted to the London Bridge hospital for a pain-relieving procedure. She ended up being paralysed within hours of a procedure for which the claimant says there was no informed consent, and the efficacy of the procedure has not been proven.

“A negligence claim is being pursued as a result. This remains an ongoing claim, which is currently being defended.”

None of the defendants in the case responded directly to the claims when approached by the Guardian, but they are contesting the allegations against them and each has filed a defence.

HCA Healthcare UK owns and runs other private hospitals in the capital besides the London Bridge, including the Wellington, Princess Grace and Lister.

A HCA spokesperson said: “In order to ensure the confidentiality of every patient we care for, we would not comment on an inquiry into any individual’s care.”

Browne Jacobson solicitors, who are representing Al-Kaisy, said that patient confidentiality meant that he could not say anything but does deny the claims. His lawyer, Matthew Trinder, added: “I can tell you that all the allegations are strenuously denied and that a full defence has been served.”

Lam did not reply to requests to respond.