Looking for input on suspected corticobasal syndrome/CBD

My grandfather is 73 and has been diagnosed with suspected corticobasal degeneration (CBD)/corticobasal syndrome. I’m trying to understand whether his presentation fits CBD closely or whether there are other possibilities we should be considering.

His symptoms have progressively worsened, particularly on the right side.

Timeline:

• Right-hand tremor was first noticed in 2023, although his more significant functional decline began in 2025.
• By 2025, he developed progressive loss of right-hand function, severe right-arm stiffness/dystonia, and difficulty performing learned movements.
• He has developed significant right-sided apraxia, including dressing apraxia. At one examination he could not mimic movements with the right hand.
• He has bilateral bradykinesia, much worse on the right, with absent right arm swing and abnormal right-arm posturing while walking.
• He has progressive gait impairment, stooped posture, shuffling/shortened stride, and postural instability/falls.
• Speech has progressively become more difficult, particularly getting words out, with earlier documentation of naming difficulty and paraphasic errors.
• An alien-limb phenomenon of the right arm was documented by one neurologist, although this was not reported at a later evaluation.
• No hallucinations, REM sleep behavior disorder, significant constipation, or major autonomic symptoms.
• He has longstanding difficulty with smell.
• He remains relatively independent cognitively and still manages finances and drives locally, although a MoCA on 8/11/26 was 18/26.

Neurologic evaluations:
His original neurologist diagnosed CBD based on the combination of asymmetric dystonia, apraxia, parkinsonism, language dysfunction, and MRI findings.

He subsequently saw another neurologist in March 2026. That neurologist independently documented severe right-arm rigidity/dystonia, marked apraxia, dressing apraxia, bilateral bradykinesia (R>L), and gait impairment, and agreed that the presentation was suggestive of corticobasal syndrome/CBD.

At the August 2026 follow-up, the diagnosis was still described as suspected corticobasal syndrome.

Levodopa response:
He has had essentially no meaningful response to carbidopa/levodopa despite a substantial trial. He was taking up to 25/100 mg, 3 tablets three times daily (>900 mg levodopa/day), and was later increased to 4 tablets TID but could not tolerate that dose. He is now tapering off.

Imaging:

• CT 9/9/25: asymmetric hypodensities involving the left frontal and left parietal subcortical/periventricular white matter, possibly representing an infarct of uncertain age.
• MRI 10/17/25: cortical volume loss and scattered periventricular/subcortical white-matter disease, reported as most likely small-vessel ischemic disease. His neurologist interpreted the cortical atrophy as worse on the left.
• MRI 1/15/26: mild-to-moderate white-matter changes without acute infarct or enhancing lesions.

Neuropsychological testing showed MCI with deficits in expressive language, processing speed, attention, and ideomotor apraxia, with a left-greater-than-right frontal-subcortical/parietal pattern. The neuropsychologist stated that the etiology was unclear and discussed FTLD/CBD, synucleinopathy, and vascular disease as possibilities.

Other medical history that may be relevant:

• Biopsy-proven celiac disease diagnosed in 2014, but he has never followed a gluten-free diet.
• Chronic B12 deficiency requiring injections.
• Chronic hyponatremia for >10 years.
• Significant cardiovascular history including aortic valve replacement and CABG.
• Progressive weight loss/frailty despite a reportedly good appetite.

His weight went from 158 lb on 10/17/25 → 151 lb on 11/6/25 → 136.8 lb on 2/10/26. He was 141 lb on 8/11/26, so he has regained some weight but remains about 17 lb below his October 2025 weight.

My questions:

1. Does this sound like a fairly classic corticobasal syndrome presentation?
2. How confidently can CBD be distinguished from other causes of CBS during life?
3. Could the left frontal/parietal vascular abnormalities contribute significantly to his right-sided motor/apraxic and language symptoms?
4. Could untreated celiac disease, B12 deficiency, chronic hyponatremia, or nutritional deficiencies contribute to the neurologic presentation or frailty?
5. Would you recommend evaluation at a tertiary movement-disorders center such as Mayo Clinic for review of the actual MRI images and the entire case?
6. Are there particular tests or imaging studies that would be useful in distinguishing CBD from vascular disease or another atypical parkinsonian disorder?

I understand that an online forum cannot diagnose him. I’m mainly trying to determine whether we should pursue a comprehensive tertiary-center second opinion and what questions we should be asking.