Parkinson's Disease

What changes during this transition

Idiopathic Parkinson's disease is a different conversation from generic 'aging brain' or 'cognitive decline.' The diagnostic frame is movement-disorder-neurologist-led with the MDS clinical criteria, and the rule-out for atypical parkinsonism (MSA, PSP, CBD, DLB) matters editorially — these are distinct diseases with distinct prognosis and distinct evidence, and conflating them is a common community-framing failure. The prodromal window — REM sleep behavior disorder, hyposmia, constipation, mood and autonomic symptoms that can precede motor onset by years — is real but is a research and surveillance conversation rather than an indication for any pharmacotherapy at the editorial cutoff. Familial subtypes (LRRK2-associated PD, GBA-associated PD with its faster cognitive trajectory) shape the conversation about genetic counseling and trial enrollment but don't change the standard-of-care backbone. The standard-of-care ladder remains levodopa-centered, with two paradigm refinements in 2024 worth naming directly. Levodopa/carbidopa has been the foundation since the 1960s and remains it; the August 2024 FDA approval of Crexont (carbidopa/levodopa extended-release capsules) and the October 2024 FDA approval of foslevodopa/foscarbidopa (Vyalev / Produodopa, 24-hour continuous subcutaneous infusion) are meaningful refinements of the levodopa-delivery problem that has shaped PD pharmacotherapy for sixty years. Vyalev in particular reshapes the conversation for advanced motor fluctuations, sitting where Duopa (levodopa-carbidopa intestinal gel via PEG-J tube) used to sit with substantially less procedural burden. Inbrija (inhaled levodopa) handles OFF episodes. Dopamine agonists (pramipexole, ropinirole, rotigotine) remain useful in younger patients with explicit impulse-control-disorder counseling (pathological gambling, hypersexuality, compulsive shopping and eating are real adverse effects). MAO-B inhibitors (rasagiline, selegiline, safinamide) and COMT inhibitors (entacapone, opicapone, tolcapone) layer for symptom and fluctuation management. Amantadine (and Gocovri extended release) addresses dyskinesia. DBS and focused-ultrasound (HIFU) thalamotomy or pallidotomy are the device-based options for advanced motor fluctuations and tremor-dominant disease. Apomorphine SC pump or sublingual Kynmobi handles rescue. Structured exercise — Tai chi, treadmill programs, forced-cadence cycling, boxing-style programs — is MDS-endorsed Tier 1 non-pharmacologic and does more for long-term motor and non-motor outcomes than most pharmacologic adjuncts. No disease-modifying therapy exists yet. Prasinezumab (anti-α-synuclein MAb) failed PASADENA. Cinpanemab failed SPARK. The α-synuclein-targeted ASO program (BIIB101) has not landed positive Phase 2/3. LRRK2 inhibitor trials (BIIB122 / DNL201) are in motion for the LRRK2-associated subtype but have not produced a registered indication. The most editorially interesting peptide-adjacent signal — and the one most at risk of community over-extension — is the GLP-1 receptor agonist class signal: Foltynie 2017 (Lancet) reported a motor-progression signal for exenatide, and the LIXIPARK trial (Meissner 2024 NEJM) reported a significant slowing of MDS-UPDRS Part III off-medication progression at 12 months on lixisenatide — the first positive Phase 2/3 readout for any drug on PD motor-progression slowing. The Rule-6 non-propagation point is load-bearing: those results are exenatide and lixisenatide specifically, NOT semaglutide. GLP-1 receptor agonists differ meaningfully across the class on CNS penetration, receptor pharmacology, weight-loss magnitude, and half-life, and the PD signal does not propagate without molecule-specific trial evidence. A semaglutide-specific PD trial program exists but no positive Phase 2/3 has reported. Where peptides fit, narrowly: semaglutide carries the most editorially interesting case as the GLP-1-class story, but the substrate frames the non-propagation problem directly and the case is for ongoing class research and a patient already on semaglutide for a metabolic indication who asks the honest question, not for adding semaglutide as a PD drug on the LIXIPARK or Foltynie evidence. Cerebrolysin's PD case is narrower than its registered dementia case — source-jurisdiction signal concentrated in cognitive non-motor and PD-with-dementia, adjunct rather than substitute for the levodopa ladder. Semax has a Russian Ministry of Health registered indication for cerebrovascular insufficiency that overlaps with cognitive non-motor symptoms in PD with cerebrovascular comorbidity, with no PD-specific registered indication in any jurisdiction. NMN and BPC-157 are honest-answer substrate-only entries — the NAD+ biology and the Sikiric-program rodent work are real research threads, but neither has a published human PD trial readout, and both are mostly community framing pulled across from adjacent contexts (general-aging, injury recovery, gut axis) without warrant.