ANSWER: C

Rationale:

Option C is correct. This patient has classic peak-dose dyskinesia (PDD): choreiform movements of the arms and trunk emerging 45 minutes post-dose during the on state, when motor function is best, resolving as the dose wears off. The previous physician's dose reduction was an error — dose reduction is not the first-line treatment for PDD and predictably worsened his motor control without meaningfully improving dyskinesia, because reducing the dose attenuates the therapeutic peak without necessarily eliminating the sensitized striatal response. The correct management is to restore the previous effective dose that provided good motor control and add amantadine as first-line pharmacological treatment for PDD. Amantadine, an uncompetitive NMDA receptor antagonist, reduces peak-dose dyskinesia by approximately 45–60% in controlled trials without a commensurate worsening of motor function — precisely the dissociation needed here. Starting at 100 mg twice daily with titration as tolerated is standard.

• Option A: Option A is incorrect; further dose reduction would deepen the motor deficit already produced by the first reduction, and PDD does not reliably resolve with progressive dose reduction — it simply trades dyskinesia for disability.
• Option B: Option B is incorrect; increasing dosing frequency at the reduced dose addresses inter-dose wearing-off but does not restore the motor benefit lost from the dose reduction, nor does it treat the underlying PDD. The falls and motor deterioration reflect reduced peak dopaminergic efficacy from the dose cut, not a timing problem.
• Option D: Option D is incorrect; adding a dopamine agonist at the reduced levodopa dose may partially compensate for motor deterioration but does not address the PDD, and the framing that keeping levodopa below the dyskinesia threshold while adding an agonist will prevent dyskinesia is pharmacologically incorrect — the sensitized striatum that drives PDD responds to dopaminergic stimulation from agonists as well as levodopa.
• Option E: Option E is incorrect; DBS evaluation is premature. This patient has not yet received appropriate first-line management for PDD — amantadine has not been tried. DBS is considered only when motor complications are refractory to optimized oral pharmacotherapy including amantadine.

ANSWER: A

Rationale:

Option A is correct. This patient's acute neuropsychiatric presentation — confusion and visual hallucinations beginning 2 days after starting amantadine — is a textbook presentation of amantadine concentration-dependent CNS toxicity from drug accumulation in the setting of renal impairment. Amantadine is excreted largely unchanged in the urine with minimal hepatic metabolism, making renal function the sole determinant of its clearance. Her CrCl of 26 mL/min places her in the 15–29 mL/min range, for which the prescribing guidance specifies every-other-day dosing or avoidance — not standard twice-daily dosing. At 100 mg twice daily in a patient with CrCl of 26 mL/min, amantadine's plasma half-life is substantially prolonged beyond the normal 10–18 hours, leading to progressive accumulation over the first few days of therapy and rising plasma concentrations that produce concentration-dependent neuropsychiatric adverse effects. In elderly patients with underlying Parkinson's disease and pre-existing vulnerability to dopaminergic and cholinergic drug effects, amantadine toxicity manifests as confusion, visual hallucinations, and agitation — exactly the presentation described. Immediate discontinuation is appropriate; with short duration of use, symptoms typically resolve within 1–2 days as the drug is cleared, though clearance will be prolonged given her renal impairment.

• Option B: Option B is incorrect; while Parkinson's disease can cause psychosis, this presentation is temporally linked to amantadine initiation with symptom onset 2 days after the drug was started — a classic timeline for accumulation toxicity. Disease-related psychosis does not begin acutely within days of a drug start in a patient with previously intact cognition. Adding quetiapine without addressing the drug toxicity would compound the problem.
• Option C: Option C is incorrect; amantadine does not cause serotonin toxicity through interaction with levodopa. Serotonin syndrome requires serotonergic agents (SSRIs, SNRIs, MAOIs, triptans) and presents with hyperthermia, clonus, and hyperreflexia — not isolated visual hallucinations and confusion.
• Option D: Option D is incorrect; while amantadine has mild anticholinergic properties, anticholinergic toxidrome at standard doses in elderly patients is not the mechanism of this presentation, and physostigmine is not the appropriate management. The primary explanation — renal accumulation causing concentration-dependent CNS toxicity — is both mechanistically correct and actionable.
• Option E: Option E is incorrect; this presentation is not idiosyncratic — it is mechanistically predictable from amantadine's pharmacokinetics in the setting of documented severe renal impairment. Halving the dose to 100 mg once daily is still substantially above the appropriate level for CrCl 26 mL/min, and 2-week monitoring without discontinuation is not appropriate management for established amantadine toxicity.

ANSWER: E

Rationale:

Option E is correct. This patient has off-period dystonia — specifically early morning and nocturnal foot dystonia reflecting the overnight levodopa nadir when plasma concentrations fall to near zero during the prolonged interval between his 10 PM and 7 AM doses. The appropriate first-line management is systemic dopaminergic optimization targeting the overnight period: adding a controlled-release carbidopa/levodopa formulation at bedtime, which releases levodopa gradually through the early morning hours and reduces the severity of the overnight trough; adding a long-acting dopamine agonist at bedtime (pramipexole or ropinirole extended-release), which provides continuous receptor stimulation bridging the overnight levodopa gap; or both in combination. This patient has had none of these interventions attempted. Botulinum toxin injection into the affected calf and foot muscles is a legitimate therapeutic option for off-period foot dystonia, but it is specifically reserved for cases refractory to optimized systemic pharmacotherapy — it addresses the symptomatic muscle overactivity without correcting the underlying dopaminergic deficit, and proceeding to it before attempting systemic optimization bypasses the more fundamental treatment. The Park-03 module explicitly places botulinum toxin in the context of systemic-measure failure, not as initial therapy.

• Option A: Option A is incorrect; botulinum toxin is not first-line for off-period foot dystonia — systemic dopaminergic optimization is, because the dystonia is driven by an addressable pharmacological deficit (overnight levodopa nadir) rather than by a fixed musculoskeletal problem that requires local intervention.
• Option B: Option B is incorrect; off-period foot dystonia is not caused by fixed structural changes in the musculature — it is a pharmacodynamic phenomenon resulting from insufficient dopaminergic stimulation in the off state. Restoring dopaminergic coverage reliably resolves the dystonic posturing in most patients, refuting the claim that myofiber changes make pharmacological optimization futile.
• Option C: Option C is incorrect; botulinum toxin injection into the foot and calf muscles for focal dystonia is not contraindicated in Parkinson's disease. The concern about swallowing dysfunction applies to injections in the cervical and pharyngeal region, not to distal lower extremity injections targeting the foot and calf.
• Option D: Option D is incorrect; initiating botulinum toxin simultaneously with pharmacological optimization is not the standard approach when systemic measures have not yet been tried. Proceeding to botulinum toxin before determining whether systemic optimization resolves the dystonia exposes the patient to an invasive procedure that may be unnecessary.

ANSWER: B

Rationale:

Option B is correct. This patient has the LCIG-associated peripheral neuropathy entity, driven by carbidopa's mechanism of depleting pyridoxal phosphate (PLP) — carbidopa forms a stable hydrazone complex with PLP, the active form of vitamin B6, impairing the transsulfuration pathway and causing homocysteine accumulation — compounded by functional B12 deficiency evidenced by the low-normal B12 of 198 pg/mL and the elevated homocysteine. The axonal pattern on nerve conduction studies, the elevated homocysteine, the absence of other identifiable causes, and the duration of LCIG therapy are all consistent with this recognized entity. The correct management is supplementation — vitamin B6 to replete PLP and restore cystathionine beta-synthase activity in the transsulfuration pathway, and vitamin B12 to address functional cofactor deficiency affecting homocysteine remethylation — while continuing LCIG. LCIG discontinuation is not required as the first response; the neuropathy is metabolic and nutritional in mechanism and is addressable with supplementation in most patients, preserving the substantial motor benefit she has achieved over 2 years. Ongoing neurological monitoring is appropriate to confirm stabilization or improvement.

• Option A: Option A is incorrect; LCIG discontinuation is not the required first step and is not standard management for LCIG-associated neuropathy. The mechanism is nutritional deficiency amenable to supplementation, and discontinuing LCIG — which has provided excellent motor control for 26 months — before attempting supplementation imposes a substantial functional cost without clinical necessity.
• Option C: Option C is incorrect; the neuropathy is not primarily driven by folate deficiency — serum folate is normal. While folate participates in homocysteine remethylation, the primary mechanism here is carbidopa-mediated B6 depletion impairing transsulfuration, with B12 deficiency as a co-contributor. High-dose folate alone without B6 and B12 does not address the carbidopa-PLP mechanism.
• Option D: Option D is incorrect; reducing the LCIG infusion rate by 30% to lower carbidopa exposure is not the established management protocol for LCIG-associated neuropathy. Supplementation is the standard intervention, and dose reduction risks compromising motor control without necessarily halting neuropathy progression given that depletion of existing B6 stores has already occurred.
• Option E: Option E is incorrect; sural nerve biopsy is not required before initiating treatment for LCIG-associated neuropathy with a clear clinical, biochemical, and temporal diagnosis. The combination of LCIG therapy, axonal neuropathy pattern, elevated homocysteine, and low-normal B12 in the absence of other etiologies provides sufficient diagnostic certainty to begin supplementation without histopathological confirmation.

ANSWER: D

Rationale:

Option D is correct. This patient meets all established core criteria for DBS candidacy: confirmed idiopathic Parkinson's disease (not atypical parkinsonism), levodopa responsiveness of 52% on formal UPDRS Part III challenge (well above the 30–33% minimum threshold), motor complications — diphasic dyskinesias — that are refractory to optimized oral therapy including dose frequency adjustment, COMT inhibition, and amantadine, intact cognition (MoCA 28/30), and no psychiatric contraindications. The DBS referral is appropriate. Regarding target selection, diphasic dyskinesia is specifically characterized by its occurrence at intermediate levodopa concentrations; the management goal is to minimize inter-dose concentration fluctuations. GPi DBS is particularly relevant for this complication because it provides direct antidyskinetic benefit at the level of the basal ganglia output nucleus, independent of levodopa dose reduction. By contrast, STN DBS achieves its antidyskinetic effect primarily through the levodopa dose reduction it permits, which — for a patient with diphasic dyskinesia — could paradoxically worsen the intermediate-concentration triggering by reducing the peak and prolonging the time spent at dyskinesia-triggering concentrations. LCIG also remains a valid option given its continuous delivery mechanism directly addressing concentration fluctuations. The neurologist should discuss both options with a multidisciplinary team.

• Option A: Option A is incorrect; diphasic dyskinesia is not a contraindication to DBS — it is one of the motor complications for which advanced therapy is indicated when oral therapy has failed. There is no guideline stating that continuous drug delivery is the only evidence-based advanced therapy for diphasic dyskinesia.
• Option B: Option B is incorrect; STN DBS does not directly suppress the intermediate-concentration dopamine receptor signaling triggering diphasic dyskinesia. STN stimulation's antidyskinetic mechanism runs through secondary levodopa dose reduction, which could be counterproductive for diphasic dyskinesia as noted above.
• Option C: Option C is incorrect; subcutaneous apomorphine infusion is not a mandatory prerequisite step before DBS evaluation — there is no guideline-mandated sequence requiring apomorphine trial before DBS referral in patients who meet DBS candidacy criteria with refractory motor complications.
• Option E: Option E is incorrect; there is no 10-year disease duration minimum for DBS candidacy in established guidelines. Disease duration is a consideration in confirming the diagnosis of idiopathic PD but is not itself a minimum threshold for DBS timing.

ANSWER: C

Rationale:

Option C is correct. Cognitive impairment is one of the core contraindications to DBS, explicitly listed in established patient selection criteria. DBS does not benefit cognition and may worsen it — the surgical procedure, stimulation effects, and postoperative adjustment period all carry neuropsychiatric risks that are substantially amplified in patients with pre-existing cognitive impairment. A MoCA score of 18/30 is in the mild-to-moderate dementia range, well below the cognitive threshold for DBS candidacy. This is not a relative contraindication to be weighed against motor benefit — it is a disqualifying criterion because the risk-benefit calculus is unfavorable when cognitive deterioration from surgery could further compromise an already-impaired patient's functional independence and quality of life. However, the contraindication to DBS does not mean advanced therapy is unavailable. This patient has refractory motor complications with good levodopa responsiveness (44% UPDRS improvement), making her an appropriate candidate for evaluation for device-aided continuous dopaminergic delivery — either LCIG via PEG-J tube (if gastrointestinal anatomy and surgical fitness are adequate) or subcutaneous apomorphine infusion (which does not require surgical tube placement and is more readily reversible). Both provide the continuous dopaminergic stimulation that addresses both off-time and dyskinesias without the cognitive risks of DBS. Caregiver support will be essential for device management given her cognitive impairment.

• Option A: Option A is incorrect; cognitive impairment of this degree is not merely a relative contraindication manageable by target selection. GPi DBS does have a more favorable cognitive and mood profile than STN DBS, but neither target is appropriate for a patient with a MoCA of 18/30 — the favorable GPi comparison applies to patients with mild pre-existing vulnerabilities, not established dementia.
• Option B: Option B is incorrect; significant cognitive impairment is explicitly listed as a contraindication to DBS in established selection criteria, not merely a risk factor to be weighed. No guideline supports proceeding with DBS at any level of baseline cognitive impairment if the deficit is significant.
• Option D: Option D is incorrect; the contraindication to DBS does not exhaust advanced therapy options. Redirecting entirely to caregiver support without evaluating continuous delivery therapy abandons a clinically meaningful treatment pathway for this patient's refractory motor complications.
• Option E: Option E is incorrect; surrogate decision-making capacity does not alter the clinical contraindication to DBS based on cognitive impairment. The issue is not consent — it is that DBS is medically contraindicated by the patient's neurocognitive status regardless of who provides consent.

ANSWER: A

Rationale:

Option A is correct. Amantadine must not be abruptly discontinued in patients on chronic high-dose therapy — the drug contributes to central dopaminergic tone through its dopamine release-enhancing and reuptake-inhibiting properties, and sudden removal precipitates an abrupt reduction in central dopaminergic activity that can produce a neuroleptic malignant syndrome-like state characterized by hyperthermia, severe lead-pipe rigidity, autonomic instability, markedly elevated CK, and altered consciousness. This is a recognized and potentially life-threatening perioperative complication when amantadine is stopped without a taper in patients taking higher doses such as this patient's 200 mg twice daily. The correct approach is to maintain amantadine throughout the perioperative period: if the patient is unable to take oral medications postoperatively, the drug should be crushed and administered via nasogastric tube until oral intake resumes. Additionally, the anesthesia team must be instructed to avoid dopamine antagonist antiemetics — particularly metoclopramide and prochlorperazine — which can precipitate NMS in PD patients by blocking central dopamine receptors in an already dopamine-depleted state. Ondansetron is an acceptable antiemetic alternative if needed, though QTc monitoring is warranted given amantadine's own QTc effects.

• Option B: Option B is incorrect; there is no established 48-hour washout protocol for amantadine that safely eliminates withdrawal risk, and 48 hours is well within the window in which NMS-like withdrawal has been reported. NMDA antagonism does not significantly interact with inhalational anesthetics in the manner described.
• Option C: Option C is incorrect; a 2-week taper before elective surgery is a reasonable general principle for dopaminergic drugs in PD, but completely stopping amantadine preoperatively is unnecessary and creates the very gap that risks withdrawal. The correct approach is to continue it through surgery, not to taper it down and stop.
• Option D: Option D is incorrect; the 5–7 day minimum before withdrawal syndrome can occur is not established — NMS-like withdrawal from amantadine has been reported within 48–72 hours of abrupt discontinuation at high doses, well within the postoperative day 2 window described.
• Option E: Option E is incorrect; memantine is not an established substitute for amantadine in Parkinson's disease management, does not have equivalent evidence for dyskinesia reduction, and cannot simply replace amantadine preoperatively. The premise that memantine has no withdrawal syndrome is not a basis for substitution.

ANSWER: E

Rationale:

Option E is correct. This patient's problems are entirely explained by the dosing timing error and are fully correctable by switching to bedtime administration. Gocovri's pharmacokinetic profile is not time-independent — it is specifically designed around the sleep-wake cycle. When taken at bedtime, the sustained-release mechanism produces low amantadine plasma concentrations during the overnight sleep period (minimizing neuropsychiatric adverse effects during sleep) and a rising concentration curve through the early morning and daytime waking hours, delivering antidyskinetic drug exposure during the period of peak levodopa-related motor activity. When taken in the morning instead, this profile is inverted: amantadine concentrations peak during the late afternoon and overnight hours, producing high concentrations during sleep that directly cause insomnia and nocturnal confusion — exactly his reported symptoms — while daytime concentrations during his active waking hours, when dyskinesias occur, remain relatively low — explaining the absence of dyskinesia benefit. Counseling should emphasize that the drug must be taken at bedtime, that his current symptoms are a predictable consequence of incorrect timing rather than a drug failure or intolerance, and that switching to bedtime administration should be expected to resolve the sleep and cognition symptoms while providing the intended dyskinesia benefit. Reassessment after 4 weeks of correct bedtime dosing is appropriate.

• Option A: Option A is incorrect; the 40% non-response rate is fabricated, and attributing the insomnia and confusion to dose-dependent toxicity independent of timing misses the straightforward timing explanation and would lead to unnecessary medication change.
• Option B: Option B is incorrect; Gocovri does not produce a peak approximately 7–8 hours after ingestion that would time the peak to the afternoon with morning dosing — the release profile produces rising concentrations through the overnight and morning hours after bedtime administration, not a mid-afternoon peak after morning dosing.
• Option C: Option C is incorrect; the pharmacokinetic profile of Gocovri is entirely dependent on the timing of administration relative to the sleep-wake cycle. Stating that the profile is independent of timing directly contradicts the pharmacological basis of the formulation's design.
• Option D: Option D is incorrect; amantadine's NMDA receptor antagonism is concentration-dependent — higher concentrations at active channels produce greater use-dependent block. Concentration independence is pharmacologically incorrect. Amantadine does not undergo hepatic accumulation; it is renally excreted unchanged.

ANSWER: B

Rationale:

Option B is correct. The wearing-off management algorithm described in the Park-03 module specifies a clear stepwise sequence based on pharmacological rationale. The first step is to shorten the dose interval — increasing from three to four or five daily doses while maintaining the current individual dose or making only modest increases — because most wearing-off in a patient who is otherwise well-controlled on their current dose represents a timing problem: the inter-dose interval exceeds the effective duration of each dose, allowing plasma levodopa to fall below the motor threshold before the next dose is taken. Shortening the interval corrects this trough without amplifying peak concentrations. The internist bypassed this step and proceeded directly to COMT inhibitor addition, which is the second-line intervention when interval adjustment alone is insufficient. With entacapone now providing pharmacokinetic benefit, the appropriate next step is to add dose frequency adjustment — increasing to four or five daily doses — since the two interventions are complementary: COMT inhibition broadens and prolongs the plasma levodopa curve per dose, while more frequent dosing reduces the inter-dose interval, together providing more complete wearing-off coverage. This patient still has persistent wearing-off despite entacapone, indicating that interval adjustment may provide additional benefit.

• Option A: Option A is incorrect; MAO-B inhibitor addition (rasagiline) is the third-line intervention in the wearing-off algorithm, providing central pharmacodynamic benefit after peripheral pharmacokinetic interventions have been optimized; it was not the bypassed first-line step.
• Option C: Option C is incorrect; switching to controlled-release carbidopa/levodopa is not the first-line intervention for wearing-off, and the evidence for CR formulations reducing wearing-off versus optimized IR dosing is modest; discontinuing entacapone because it is "redundant" with CR formulations is pharmacologically incorrect — they act through different mechanisms at different steps.
• Option D: Option D is incorrect; entacapone is not the recommended first step in the established wearing-off management algorithm — dose interval shortening is specified as the first intervention, with COMT inhibitor addition as the second step when interval adjustment alone is insufficient.
• Option E: Option E is incorrect; adding a long-acting dopamine agonist is a later-stage intervention for wearing-off refractory to oral optimization, not the first-line step. Agonists are added when optimized levodopa scheduling and adjunctive agents have been insufficient.

ANSWER: D

Rationale:

Option D is correct. Severe dysphagia with documented aspiration is a recognized relative contraindication to LCIG via PEG-J tube for two related reasons. First, PEG placement requires upper gastrointestinal endoscopy — a procedure that carries aspiration risk during scope passage and sedation in a patient who already aspirates thin and thick liquids and has had two aspiration pneumonia admissions; the endoscopic component creates procedural aspiration risk that is substantially elevated in this patient. Second, ongoing severe dysphagia creates an ongoing aspiration risk around the PEG site from oral secretions and any oral intake, and dysphagia can impair the patient's ability to manage tube care complications. In this clinical context, subcutaneous apomorphine infusion is the appropriate alternative continuous delivery approach. Apomorphine is a high-potency dopamine agonist (stimulating both D1 and D2 receptors) delivered via a programmable subcutaneous pump that bypasses the gastrointestinal tract entirely, carrying no aspiration risk from the delivery mechanism itself. It does not require endoscopic or surgical implantation and is more readily reversible than LCIG or DBS. The principal management challenges — injection site nodules and necrosis, nausea requiring domperidone pretreatment, and neuropsychiatric monitoring — are manageable in a cognitively intact patient with good caregiver support.

• Option A: Option A is incorrect; the aspiration risk is highly relevant to PEG-J placement. While PEG insertion is percutaneous, it requires upper endoscopy with sedation and airway management that carries substantially elevated aspiration risk in a patient with severe oropharyngeal dysphagia and a history of aspiration pneumonia.
• Option B: Option B is incorrect; radiologically guided PEG placement can avoid oral endoscopy, but the ongoing severe dysphagia with aspiration around the external tube and the patient's established aspiration risk still constitute significant concerns that make LCIG a higher-risk choice when an effective non-gastrointestinal alternative exists.
• Option C: Option C is incorrect; DBS is not the only remaining option when LCIG is contraindicated — subcutaneous apomorphine infusion is an established alternative continuous delivery approach that is specifically appropriate when gastrointestinal or surgical delivery is not feasible. Presenting DBS as the default when LCIG is unavailable ignores this option.
• Option E: Option E is incorrect for the same reason as C — GPi DBS is a valid option for this patient given his intact cognition and adequate levodopa response, but it is not the automatic default when LCIG is relatively contraindicated. Subcutaneous apomorphine should be considered and discussed with the patient as a less invasive first choice before proceeding to surgery.

ANSWER: C

Rationale:

Option C is correct. This patient has developed a clinically significant major depressive episode with passive suicidal ideation in the post-STN DBS period, driven by two converging pharmacological mechanisms that the clinical team must address simultaneously and urgently. First, the severity of symptoms — passive suicidal ideation, functional impairment, and 6 kg weight loss — requires urgent psychiatric evaluation; this is not a self-limiting adjustment reaction and carries meaningful risk. Second, the two pharmacological contributions must be identified and managed: bilateral STN DBS carries a recognized risk of mood and neuropsychiatric adverse effects including depression, attributed to stimulation of limbic STN subdivisions or current spread to adjacent limbic circuitry; DBS programming review to assess whether stimulation parameters (electrode contact, amplitude, frequency) can be adjusted to reduce limbic involvement is appropriate. Concurrently, the 55% levodopa dose reduction imposed postoperatively has withdrawn a substantial dopaminergic contribution to the mesolimbic and mesocortical pathways — the dopamine projections from the ventral tegmental area that support mood, motivation, and anhedonia resistance. In a patient who has developed significant depression, partial restoration of levodopa toward pre-operative levels should be considered to reverse the dopaminergic withdrawal contribution to mood, accepting modest dyskinesia re-emergence if necessary to support psychiatric recovery. This multi-pronged response — urgent psychiatry, levodopa partial restoration, DBS parameter review — addresses all contributing mechanisms.

• Option A: Option A is incorrect; passive suicidal ideation is not a symptom that should be monitored with a 6-week follow-up and reassurance. This represents clinically urgent psychiatric pathology requiring immediate evaluation and intervention.
• Option B: Option B is incorrect; while antidepressants have a role in post-DBS depression management, attributing the depression exclusively to a manageable antidepressant-treatable condition without addressing stimulation parameters or levodopa reduction ignores the specific pharmacological mechanisms at play and delays addressing potentially modifiable contributors.
• Option D: Option D is incorrect; immediately deactivating the DBS device is not the appropriate management for post-operative depression. DBS deactivation would abruptly withdraw motor benefit and could precipitate severe motor deterioration; parameter adjustment by the programming team — not device deactivation — is the appropriate stimulation-related intervention.
• Option E: Option E is incorrect; carbidopa/levodopa does not have antidepressant properties in the traditional sense, and the interaction between full levodopa doses and STN stimulation does not make them unsafe to co-administer — dose reduction is a clinical choice to manage dyskinesias, not a safety requirement.