I am Dr Jim Cromwell, MA(Hons) PsychD CPsychol MRSLI. I am a chartered clinical psychologist working with deaf people for sixteen years.

A specialist neurology clinic for deaf people is vital for a number of key reasons:

1. Hearing people have a lot of auditory cortex, but it is auditory only superficially due to connection to the auditory nerve and is fundamentally auditory only due to its continued processing of auditory stimuli during the early years. For profoundly deaf people this cortex is quickly repurposed to other functions. 
2. For the above reason, and also importantly due to the use of British Sign Language (BSL) as the native language of communication and of THOUGHT, the neurological architecture of deaf people cannot be assumed to be similar to that of hearing people.
3. Clinically, for reasons of using a language with a visual grammar, and for reasons of differing neuro-architecture, a deaf patient's neurocognitive functioning cannot be assumed to be based upon the same modular cognitive skill-sets as hearing patients. For example the useful distinction of verbal/auditory and visual memory is meaningless for a deaf patient, and the relationship between motor cortex and language production will be stronger. "Subvocalisation" becomes very different indeed, and so on. 
4. Neurocognitive instruments are based upon studies of the factor structure of hearing people's cognitive function, but these are invalid and misleading for deaf people. It has been documented repeatedly in the deafness literature that hearing doctors when faced with a deaf patient with whom communication is difficult (including when effectively and appropriately interpreted) rely heavily on these instruments as they appear to be more scientifically robust, when in truth they are dangerously invalid for this group. A specialist centre will be able to recognise and avoid these pitfalls, as well as generate appropriate instruments.
5. BSL-English interpreted clinical interviews, even at the highest level of competence, yield difficulties that are invisible to the generic-services neurologist and neuropsychologist. Good interpretation of well-formed BSL into well-formed English inevitably also interprets deaf cognitions as hearing ones, masking the important differences for clinicians. Also, neurocognitively impaired deaf people will present with specific language impairments which are impossible to identify via interpretation unless the neuro-clinician is themselves fluent in BSL, or if the interpreter is neuropsychiatrically trained.
6. Opportiunities for rehabilitative interventions are far reduced for deaf patients, since group interventions are impossible for deaf people in groups of hearing people, and ineffective when accompanied by an interpreter (and also decreasingly effective for the hearing people in that group due to the changed fluidity of the interactions). A specialist centre will be better placed to construct groups of similarly-impaired deaf people due to the increased incidence of those neuroimpairments presenting to clinic. Signing clinicians would be able to run rehab groups comparable to those provided for hearing people.
7. Equally one-to-one interventions are more effectively implemented when provided directly in BSL, than via interpretation.