Hydrocephalus and Rapidly Progressing Hearing Loss

I am writing on behalf of someone who is not a member here, but suffering greatly right now and would appreciate input, opinions and maybe even experience.

He is in his early 20s and has had tinnitus for 6,5 years, but had a worsening 2 years ago which made his manageable tinnitus debilitating. His sound is around 1500 Hz, and MML is around 70 dB.

What makes him seek advice is that he is experiencing rapid hearing loss, his threshold in the 1500-2000 Hz range deteriorates 10-15 dB every couple of months since the worsening without apparent reason. He tried hearing aids (only unilateral, because insurance only covered that), IV steroids, CBT, Piracetam, Betahistine.

Which complicates things: He has hydrocephalus, which is probably congenital, but only caused symptoms at 10 yo. (It may also be acquired as he caught an unspecified infection as a newborn.) He lives with a shunt. Doctors are generally divided on the issue whether his hydrocephalus could be the root cause of the progressive hearing loss. Neuro says it's an ENT issue and vice versa.

I know that his case is kind of unique due to his condition, but I would like to ask what other problems could cause rapid, sensoneural hearing loss?

He suspects that he may have been infected with Bartonella. If so, could that cause hearing related issues?