Serotonin syndrome vs neuroleptic malignant syndrome — distinguishing these drug-induced emergencies is one of the highest-value clinical differentials in pharmacology. Both cause hyperthermia, altered consciousness, and movement abnormalities — but the causative drugs, mechanisms, and specific clinical features differ critically. Serotonin syndrome: excess serotonergic activity (SSRIs + MAOIs, tramadol, fentanyl, triptans, lithium, linezolid, MDMA). Clinical: hyperreflexia + clonus (the pathognomonic feature — spontaneous rhythmic oscillations at the ankle or knee) + agitation + myoclonus + tremor. Onset: hours. NMS: dopamine blockade (antipsychotics, metoclopramide). Clinical: lead-pipe rigidity (uniform resistance throughout passive limb movement) + bradykinesia + markedly elevated CK + autonomic instability. Onset: days-weeks. The bedside test: elicit ankle clonus (dorsiflex the foot briskly and sustain the dorsiflexion — sustained clonus = SS). Test lead-pipe rigidity (passively flex/extend wrist — uniform ratchet resistance throughout range = NMS, not just at initiation). Both are treated by stopping the causative drug and hospital admission, but SS specifically benefits from cyproheptadine (5-HT2A antagonist) while NMS benefits from dantrolene and bromocriptine. Wilson's disease is the diagnosis most commonly missed in young adults with tremor — average time from symptom onset to diagnosis is 1–4 years. The disease is entirely treatable with copper chelation (penicillamine or trientine) or zinc supplementation if caught early; missed diagnosis causes irreversible hepatic and neurological damage.

The alcohol test for essential tremor — small amounts of alcohol (1 unit) reliably improve essential tremor in approximately 50–70% of patients for 30–45 minutes. The mechanism is GABA-A receptor modulation by ethanol in the olivocerebellar circuits that generate pathological oscillation. This has two important clinical implications: (1) a positive history of alcohol-responsive tremor strongly supports ET diagnosis (Parkinson's resting tremor does NOT improve with alcohol); (2) many ET patients self-medicate with alcohol, explaining heavy or dependent drinking patterns in some patients. The GP should ask about this directly and non-judgmentally: 'Some people with this type of tremor find that alcohol makes it better — is that the case for you?' A positive response confirms ET and opens a conversation about the risks of alcohol self-medication. The sodium oxybate (Xyrem) mechanism for ET treatment is related to this alcohol-GABA connection: sodium oxybate is the sodium salt of gamma-hydroxybutyrate (GHB), which acts on GABA-B receptors, producing similar olivocerebellar inhibition without the hepatotoxic and addiction risks of alcohol.

Wilson's disease serology interpretation: caeruloplasmin is the copper-carrying protein synthesised in the liver — it is low in Wilson's disease because the mutant ATP7B protein cannot incorporate copper into caeruloplasmin before secretion, causing both low caeruloplasmin (<200 mg/L in 80% of Wilson's) and free copper accumulation in tissues. However, caeruloplasmin is an acute-phase reactant — it can be falsely normal or elevated during inflammation, pregnancy, or OCP use. The 24-hour urine copper is a more sensitive test (>100 mcg/24h is abnormal; >40 mcg/24h is borderline). The Kayser-Fleischer ring is the most specific clinical sign — it is visible at the periphery of the cornea as a golden-brown arc on slit-lamp examination in approximately 95% of neurological Wilson's cases. GPs do not need a slit lamp to suggest this diagnosis — request ophthalmology review for slit-lamp examination in any young patient with unexplained neurological symptoms + liver disease. Functional tremor (functional movement disorder, FMD) is increasingly recognised as a common diagnosis in neurology clinics — it accounts for approximately 5–10% of all new neurology referrals for tremor. The traditional view that functional tremors are 'psychosomatic' or 'not real' has been superseded by neuroimaging evidence of genuine abnormal motor control mechanisms. GPs should refer to neurology with this diagnosis in mind rather than labelling patients as 'anxious' or 'seeking attention'.

The re-emergent tremor of Parkinson's disease is one of the most clinically useful diagnostic findings — when a patient with PD holds their arms outstretched, the resting tremor (which is present at rest and suppressed by initiating movement) initially disappears. However, after 5–15 seconds of sustained posture, the tremor re-emerges at the same frequency as the resting tremor (3–6 Hz). This re-emergent postural tremor of PD is distinct from the immediately-appearing postural tremor of essential tremor and is a key diagnostic discriminator. GPs who observe this re-emergent pattern during posture-hold testing should record it explicitly — it supports a Parkinson's diagnosis and justifies prompt neurology referral. NICE NG71 (Parkinson's disease, 2017) specifies that a GP who suspects Parkinson's should refer urgently to a clinician with specialist expertise in movement disorders BEFORE initiating any dopaminergic treatment. This is because the distinction between PD and Parkinson's-plus syndromes (MSA, PSP) is a specialist-level clinical assessment — empirical levodopa before specialist confirmation is poor practice. The only exception: if specialist waiting time is very long (>4 months) and symptoms are significantly disabling, a GP may cautiously initiate levodopa/carbidopa in consultation with the neurology team.

NICE NG71 referral before medication initiation for Parkinson's disease protects patients from two specific harms: (1) Starting levodopa in a patient who has MSA or PSP — both of which initially resemble PD but respond poorly to levodopa and have worse prognosis. Initiating levodopa empirically in MSA gives a false reassurance that the patient has PD, delays the correct diagnosis, and exposes the patient to medication that will not significantly help them. (2) Missing an atypical presentation of a tumour, vascular disease, or drug-induced parkinsonism that requires different investigation and management. The specialist assessment typically takes 30–60 minutes and includes: careful history (onset symmetry, falls early in course, eye movement abnormalities for PSP), examination (pull test for postural instability, downward gaze palsy for PSP, cerebellar signs for MSA), and often DaTSCAN (dopamine transporter SPECT scan) to confirm dopaminergic deficit. The DaTSCAN differentiates Parkinson's from essential tremor (both have clinical tremor but only PD has reduced striatal dopamine transporter uptake) but cannot distinguish PD from other parkinsonian syndromes.

The propranolol NNT for essential tremor (approximately 3) is one of the most favourable treatment effect sizes in neurology — meaning for every 3 patients treated with propranolol, one achieves clinically meaningful tremor reduction they would not have achieved without treatment. In practice, approximately 50–60% of ET patients respond to propranolol with approximately 50% amplitude reduction, which is sufficient to enable normal daily activities (holding a cup steadily, writing legibly, applying makeup, eating without spilling). The non-responders to propranolol (approximately 40%) should be offered primidone — the two drugs work via different mechanisms and a non-responder to one may respond to the other. Primidone is converted to phenobarbitone in the liver, which enhances GABA-A-mediated inhibition; propranolol works via beta-2 receptor antagonism reducing peripheral tremorgenic signalling. Combining both at lower doses can provide additive benefit with fewer side effects than high-dose monotherapy. The performance anxiety tremor use case (single 40 mg propranolol before a high-stakes event) is well-evidenced in musicians, surgeons, public speakers, and examinees, and is an appropriate off-label prescribing decision that GPs can make — it has an excellent safety profile for occasional use.

Focused ultrasound thalamotomy (FUS-T) is a transformative non-invasive procedure for essential tremor that was approved by NICE (IPG438) in 2016 and represents a major advance for patients with severe disabling unilateral ET who have failed or cannot tolerate propranolol and primidone. The procedure uses 1024 ultrasound transducers focused through the intact skull onto the VIM nucleus of the thalamus — the focused convergence of sound waves creates precise tissue heating at the target, ablating the thalamic oscillator circuit responsible for ET without any incision or implanted hardware. The result is immediate tremor abolition in the treated hand (the dominant hand is typically treated first). The limitation is that bilateral treatment carries significant risks of dysarthria and gait ataxia, so most patients are treated unilaterally. GPs should be aware of FUS-T as a referral option for patients with severe ET — it is available at several NHS centres including King's College Hospital, Salford Royal, and others, and is available to appropriately selected patients.

The DVLA notification obligation for Parkinson's disease is a legally mandatory requirement that GPs must communicate and document — any person diagnosed with Parkinson's disease must notify the DVLA (using form V1 online or paper form). The DVLA will then assess fitness to drive individually, typically initially granting a licence with a 1–3 year review period, with conditions. The GP's obligation is to: (1) advise the patient of this requirement at or shortly after diagnosis; (2) document in the clinical record that this advice was given; (3) advise the patient not to drive if they develop symptoms that affect driving safety (significant tremor, dyskinesias, cognitive impairment, excessive daytime sleepiness from dopaminergic medications) and to notify the DVLA again if their condition deteriorates. The GP should not simply rely on the patient to self-notify — if a patient has not notified the DVLA within 6 weeks of being advised to do so, the GP should follow up. Failure to notify the DVLA is a criminal offence. In the rare situation where a patient continues to drive despite being advised they should not, the GP has a duty to inform the DVLA directly after warning the patient of the intention to do so.

The lithium toxicity-tremor connection is an important prescribing safety point — lithium has a narrow therapeutic range (0.6–1.0 mmol/L for maintenance), and tremor is one of the earliest signs of both therapeutic and toxic levels. A fine postural hand tremor at therapeutic levels is expected and common (approximately 30–40% of lithium patients). However, worsening tremor should always prompt a serum lithium level check — a level above 1.5 mmol/L indicates significant toxicity, with neurological features (coarse tremor, ataxia, confusion, seizures) becoming more prominent above 2.0 mmol/L. The most common causes of lithium toxicity in primary care are: dehydration (vomiting, diarrhoea, hot weather — reduced renal clearance), new prescription of NSAIDs or ACE inhibitors (both reduce renal lithium clearance), sodium-restricted diets (reduced sodium → compensatory lithium retention), and use of diuretics. Any patient on lithium who presents with worsening tremor should have a lithium level checked that day — not at next routine monitoring date.