Differentials
Cocaine use disorder
SIGNS / SYMPTOMS
Signs and symptoms are similar but shorter in duration.
Half-life of cocaine is about 1 hour, but that of methamphetamine is 12 hours. Amfetamine-type substances are therefore used fewer times per day.
INVESTIGATIONS
Confirmation with gas chromatography and mass spectroscopy (GC/MS) analysis. Considered the most specific and sensitive test. Will determine the exact compounds and presence of metabolites.
Malignant hypertension
SIGNS / SYMPTOMS
Usually a history of hypertension and a lack of central nervous system stimulation, which is common in amfetamine/methamphetamine toxicity.
INVESTIGATIONS
A negative urine toxicology test differentiates a hypertensive crisis from a drug use symptom.
Anticholinergic drug exposure
SIGNS / SYMPTOMS
History of ingestion with absent or decreased bowel sounds and dry mucous membranes, not present with stimulant use.
INVESTIGATIONS
A negative urine toxicology screen with a positive screen for anticholinergics provides differentiation.
A positive response to the cholinesterase inhibitor physostigmine test suggests anticholinergic drug use.
Neuroleptic malignant syndrome
SIGNS / SYMPTOMS
May be a history of neuroleptic exposure.
May respond to bromocriptine.
INVESTIGATIONS
Urine toxicology screen is negative for amfetamine/methamphetamine, unless there is concomitant use.
Serotonin syndrome
SIGNS / SYMPTOMS
May co-exist, e.g., if there is co-exposure to another serotonin-mediated drug, such as a monoamine oxidase inhibitor or a selective serotonin-reuptake inhibitor.
May be rapid onset after administration of a serotonergic drug.
May be hyperreflexia, clonus, diarrhoea.
INVESTIGATIONS
Urine toxicology screen is negative for amfetamine/methamphetamine, unless there is concomitant use.
Malignant hyperthermia
SIGNS / SYMPTOMS
History of recent general anaesthesia or receipt of muscle blockers.
May be a family history of similar episodes.
Responds to dantrolene sodium.
INVESTIGATIONS
Urine toxicology screen is negative for amfetamine/methamphetamine, unless there is concomitant use.
Phaeochromocytoma
SIGNS / SYMPTOMS
Paroxysmal symptoms without a history of amfetamine/methamphetamine use.
INVESTIGATIONS
Characterised by recurrent hypertensive episodes with negative urine toxicology screens.
Suggested by marked elevation of unconjugated catecholamines, metanephrines, and vanillylmandelic acid in the 24-hour urine collection test.
Thyrotoxicosis/thyroid storm
SIGNS / SYMPTOMS
Change in appetite, weight loss, sweating and heat intolerance, oligomenorrhoea, goitre, lid lag, exophthalmos, proximal muscle weakness, tremor; thyroid storm causes high fever and coma
INVESTIGATIONS
Thyroid function testing; elevated free thyroxine and/or free triiodothyronine; suppressed thyroid-stimulating hormone.
Urine toxicology screen is negative for amfetamine/methamphetamine, unless there is concomitant amfetamine use.
Schizophrenia
SIGNS / SYMPTOMS
May co-exist. Acute intoxication of amfetamine/methamphetamine may cause paranoid ideation, and auditory and tactile hallucinations, which the individual often (but not always) recognises as a drug effect. Psychotic symptoms due to methamphetamine may sometimes last for months or years after cessation of substance use. History of psychiatric illness and previous neuroleptic treatment without a history of amfetamine/methamphetamine use suggests schizophrenia.
INVESTIGATIONS
Urine toxicology screen is negative for amfetamine/methamphetamine, unless there is concomitant use.
Depression
SIGNS / SYMPTOMS
May co-exist. History of previous episodes of depression often with previous antidepressant therapy suggests depression. Withdrawal states are associated with intense depressive symptoms that can resemble a major depressive episode. Depressive symptoms attributable to stimulant withdrawal typically resolve within 1 week.
INVESTIGATIONS
Urine toxicology screen for amfetamine/methamphetamine is negative, unless there is concomitant amfetamine use.
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