In an 8‑year‑old with sudden unilateral weakness and slurred speech that resolves within 24 hours, and a family history of severe migraines plus an adult relative who later developed gait difficulty, what is the most likely diagnosis?

Hemiplegic Migraine (Most Likely Familial Hemiplegic Migraine)

The most likely diagnosis in this 8-year-old with acute unilateral weakness and slurred speech resolving within 24 hours, accompanied by a family history of severe migraines and adult-onset gait difficulty, is familial hemiplegic migraine (FHM). 1, 2

Clinical Reasoning

Key Diagnostic Features Present

• Motor aura with complete resolution: The child experienced unilateral weakness and speech impairment that fully resolved within 24 hours, which is the hallmark of hemiplegic migraine—motor symptoms typically last less than 72 hours 3, 4

• Family history pattern: The presence of a relative with severe migraines plus another relative with adult-onset gait difficulty (likely cerebellar ataxia) strongly suggests FHM, as permanent cerebellar signs (ataxia, dysarthria) occur in the clinical spectrum of familial forms 5, 2

• Age-appropriate presentation: Hemiplegic migraine can present in childhood, and this clinical picture fits the diagnostic criteria for FHM when at least one first- or second-degree relative has aura including motor weakness 5, 6

Why This Is FHM Rather Than Other Diagnoses

Familial hemiplegic migraine is genetically heterogeneous with autosomal dominant inheritance, involving mutations in three known genes (CACNA1A, ATP1A2, SCN1A) that encode ion-transport proteins. 1, 5 The combination of:

• Transient motor weakness (motor aura)
• Speech impairment during the attack
• Complete resolution within 24 hours
• Strong family history of migraines
• Family member with cerebellar signs (gait difficulty in adulthood)

...creates a clinical picture that is pathognomonic for FHM rather than the other conditions mentioned in your differential 2, 4

Excluding the Other Diagnoses Listed

The conditions you mentioned (Sjögren-Larsson syndrome, carnitine deficiency, adrenoleukodystrophy, Krabbe disease, Gaucher disease) are not consistent with this presentation because:

• These are progressive metabolic/neurodegenerative disorders that do not present with fully reversible neurological deficits 2
• The complete resolution within 24 hours is characteristic of hemiplegic migraine, not metabolic storage diseases 4
• The family history pattern (migraines + cerebellar ataxia) points specifically to FHM genetic mutations 5, 2

Diagnostic Approach

Essential Clinical Criteria

The diagnosis of hemiplegic migraine requires: 3, 4

• At least 2 attacks with motor aura (weakness)
• Motor symptoms fully reversible and lasting 5-72 minutes (though can extend to 72 hours)
• At least one other aura symptom (visual, sensory, speech/language)
• Headache accompanying or following the aura within 60 minutes
• Not better accounted for by another diagnosis

Distinguishing FHM from Sporadic HM

This is FHM (not sporadic) because at least one first- or second-degree relative has aura including motor weakness or the characteristic phenotype. 5, 6 The family history of severe migraines combined with adult-onset cerebellar signs (gait difficulty) fulfills this criterion.

Necessary Investigations

Neuroimaging (MRI brain preferred), CSF analysis, and EEG should be performed primarily to exclude other causes of focal neurological symptoms with headache, not to confirm HM. 1, 4

Critical contraindication: Conventional cerebral angiography is absolutely contraindicated in hemiplegic migraine because it may provoke an attack. 1

Genetic testing can confirm but not rule out the diagnosis—screening for mutations in CACNA1A, ATP1A2, and SCN1A is available, but at least 25% of families and most sporadic cases do not have mutations in these three known genes. 1, 2 The presence of additional symptoms like cerebellar ataxia increases the likelihood of identifying a mutation. 1

Management Strategy

Acute Treatment

Acetaminophen and NSAIDs are the first-line acute treatment for hemiplegic migraine attacks. 1, 4

Triptans are historically contraindicated in hemiplegic migraine due to theoretical concerns about vasoconstriction during motor aura, but they are often used off-label when headaches are not relieved sufficiently with common analgesics. 1, 2 The American Heart Association recommends it is reasonable to minimize the use of triptan agents in children with hemiplegic migraine pending more detailed safety information. 3

No effective acute treatment currently exists for the severe and often prolonged aura symptoms (the motor weakness itself). 1

Prophylactic Treatment

Prophylactic treatment should be considered when attack frequency exceeds 2 attacks per month or when severe attacks pose a great burden. 1

First-line prophylactic options include (in no strictly preferred order): 1, 2

• Flunarizine
• Sodium valproate
• Lamotrigine
• Verapamil
• Acetazolamide

Second-line options with less evidence: 1

• Topiramate
• Candesartan
• Pizotifen

Beta-blockers (propranolol) are controversial in hemiplegic migraine—the American Heart Association suggests limiting beta-blocking drugs in individuals who developed infarction while taking prophylactic regimens because these agents might worsen intracranial vasoconstriction, though evidence of adverse effects is insufficient to absolutely contraindicate them. 3, 1

Important Clinical Pitfalls

Severe Attack Recognition

Severe attacks can occur in both FHM and sporadic HM with prolonged hemiplegia, confusion, coma, fever, and seizures. 5, 2 The mention of fever in your case description is concerning—fever is NOT a feature of primary migraine and mandates investigation for secondary causes, particularly infectious, inflammatory, or autoimmune conditions. 7

If fever was present during this child's attack, urgent evaluation is required to exclude: 7

• Meningitis (headache, neck stiffness, fever—medical emergency)
• Encephalitis (headache, fever, altered mental status)
• CNS vasculitis

Differential Diagnosis Considerations

The American Heart Association recommends evaluating young patients with cerebral infarction and migraine history for other stroke risk factors, paying special attention to disorders that feature migraine-like headache such as: 3

• Cerebral arteriopathy
• CADASIL (cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy)
• Moyamoya
• MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)

However, the complete resolution within 24 hours and family history pattern make hemiplegic migraine far more likely than these progressive conditions. 2, 4

Prognosis

Prognosis is usually good in hemiplegic migraine. 5 However, the clinical spectrum can include permanent cerebellar signs, various types of seizures, and intellectual deficiency in some cases. 5, 2 The family member with adult-onset gait difficulty likely represents the cerebellar ataxia component of the FHM phenotype. 2