“Joost (van der Westhuizen) has failed to respond favourably and his neurological symptoms persist but he remains stable.
Consequently, the diagnosis of Motor Neuron Disease remains a probability,” said Pearl.
It was revealed last month that Van der Westhuizen, 40, was suffering from a life threatening neural disease, but Pearl said it had not yet been fully diagnosed.
“Joost (van der Westhuizen) and I will be travelling to the leading international centre of Neurology at Cleveland Medical Centre in Cleveland, Ohio, USA towards the end of July.
“There we will consult world-leading experts and researchers to assist in finalising Joost’s diagnosis and to guide further management,” added Pearl.
Van der Westhuizen, a former scrumhalf, at one stage held the record for the most Springbok Test appearances.
He retired from international rugby in 2003.