Son's desperate plea for help in finding his mum Dr Nathalie Casal after she vanished in Western Australia four months ago

The son of a retired doctor who has been missing for more than four months in Western Australia has issued a desperate plea for the public to help find his mum. 

Dr Nathalie Casal, 71, has not been seen since early December, having told her family she was going to walk the Bibbulmun Track, which runs from Kalamunda in the east of Perth to Albany and is more than 1,000km long. 

But her son, Ramon Casal, now says there have been some misconceptions about the case, which are hampering the search for his mum. 

'My mother was last seen alive at her home in Gnangara on December 6, 2023,' he told Daily Mail Australia.

'After over a month of investigations, police have reported no actual evidence to my family that (she) visited the Bibbulmun Track or started the hike she claimed to be planning.' 

Mr Casal said his mum is 'an extremely climate-conscious environmentalist' and told the police when he reported her missing on March 7 that he doubted she would have gone hiking on the Bibbulmun Track during bushfire season.

'Nobody has come forward to state that they drove my mother to the Bibbulmun Track, and she owned no car. 

'She sold her vehicle months before, for reasons she didn't explain to the family,' he said.

Dr Casal's only way of getting around was a lime-green foldable bicycle, borrowed from a family member.

The bike was not found at her home in Gnangara when police and family searched it. 

Her son said: 'She was very fond of black cockatoo habitats in the Gnangara Pine Plantation and near Yanchep and Pinjar (which) are within bicycle distance of her home. 

'We would be very appreciative if locals near those areas searched the bush for possible answers, since there's a lot of ground to cover.'

In a tragic update, Mr Casal said it was only after the missing person investigation was opened that the family discovered she 'had been hiding a serious health condition which she had been diagnosed with in 2022. 

'She told no close relatives about it, but three people have confirmed that she shared the diagnosis with them.'

He said 2022 was also the year that she suddenly retired from medical practice without any explanation. 

'We do not know what her illness's last status was, or how much treatment she underwent for it. 

'It is important for any doctors who diagnosed or treated her to reach out to police,' Mr Casal said. 

'The case remains unsolved and my family is in a very stressful state of legal limbo, unable to take care of my mother's property. 

'By making more current information available, we hope that locals might look closer in the right places.'

Dr Casal is described as being approximately 157cm tall, of a slim build, with short grey hair and brown eyes.

Anyone who has seen her or has any information about her where she is, is urged to contact police immediately on 131 444.