In a 7‑month‑old infant with regression of social interaction, low activity, fatigue, and brief repetitive neck flexion followed by trunk and limb extension lasting 1–2 seconds, and an EEG showing slow background activity with multifocal spikes (no hypsarrhythmia), what is the most likely diagnosis: juvenile myoclonic epilepsy, infantile spasms (West syndrome), or Lennox‑Gastaut syndrome?

Diagnosis: Infantile Spasms (West Syndrome) - Option B

The clinical presentation of a 7-month-old infant with developmental regression, repetitive brief neck flexion followed by trunk and limb extension lasting 1-2 seconds in clusters, and an EEG showing slow waves with multifocal spikes is diagnostic of infantile spasms (West syndrome), even in the absence of classic hypsarrhythmia. 1, 2

Clinical Reasoning

Age and Presentation Match Infantile Spasms

• Peak age of onset for infantile spasms is 4-7 months, making this 7-month-old patient precisely within the typical window 2
• The described movements—brief (1-2 seconds) neck flexion followed by trunk and limb extension occurring in a repetitive pattern—are classic epileptic spasms that define this syndrome 1, 2
• Developmental regression (stopped smiling, low activity, fatigue) is a core feature of West syndrome and strongly supports this diagnosis 1, 2

EEG Findings Support the Diagnosis

• While hypsarrhythmia is the most characteristic EEG pattern, infantile spasms can occur without hypsarrhythmia (termed "ISW" - infantile spasms without hypsarrhythmia), which is a recognized variant 1
• The presence of slow background activity with multifocal spikes is consistent with the epileptic encephalopathy seen in infantile spasms 1, 2
• Current terminology recognizes that hypsarrhythmia is no longer absolutely required for the diagnosis of infantile spasms syndrome 1

Why Not the Other Options?

Juvenile Myoclonic Epilepsy (Option A) is excluded because:

• This syndrome typically begins in adolescence (ages 12-18 years), not infancy [@general medical knowledge@]
• The seizure semiology described does not match myoclonic jerks characteristic of JME [@general medical knowledge@]

Lennox-Gastaut Syndrome (Option C) is excluded because:

• LGS typically has onset between 3-5 years of age, not at 7 months 3
• LGS is characterized by multiple seizure types including tonic seizures (which may appear late), not the brief flexion-extension spasms described 3
• Many cases of LGS actually evolve from infantile spasms, representing a later stage rather than the initial presentation 3, 4
• The age and clinical picture here represent the earlier infantile spasms phase, not the later LGS evolution 4

Critical Diagnostic Pitfall

The absence of hypsarrhythmia should NOT exclude the diagnosis of infantile spasms. The current understanding recognizes infantile spasms syndrome as a broader spectrum that includes variants without classic hypsarrhythmia 1. The combination of appropriate age, characteristic spasm semiology (brief flexion-extension movements in clusters), and developmental regression are sufficient for diagnosis even when EEG shows multifocal spikes rather than hypsarrhythmia 1, 2.

Immediate Management Implications

• Urgent neuroimaging with MRI (with diffusion-weighted imaging) is the gold standard to identify underlying etiology 5
• First-line treatment options include ACTH or vigabatrin, with evidence supporting both as effective therapies 2, 6
• Early treatment is critical: shorter lag time to treatment initiation significantly improves neurodevelopmental outcomes 7, 2, 6
• Consider tuberous sclerosis as a potential etiology, which would favor vigabatrin as the preferred treatment 7