What is the likely diagnosis for a 10-year-old male child presenting with ascending paralysis, decreased tone in upper and lower limbs, brisk reflexes in the lower limb, and flexor plantar response?

Guillain-Barré Syndrome (GBS) with Preserved Reflexes

The most likely diagnosis is Guillain-Barré syndrome (GBS), specifically the acute motor axonal neuropathy (AMAN) variant, which uniquely can present with preserved or even brisk reflexes despite ascending paralysis. 1, 2

Key Diagnostic Features Supporting GBS

The clinical presentation of ascending paralysis with decreased tone is classic for GBS, which is the most common cause of acquired paralysis in children in countries where poliomyelitis has been eliminated. 3 The critical distinguishing feature here is the presence of brisk reflexes in the lower limbs, which occurs specifically in the pure motor variant with AMAN subtype on electrophysiological examination. 1

Why Brisk Reflexes Don't Exclude GBS

• In typical GBS, reflexes are decreased or absent in most patients at presentation. 1
• However, in a minority of patients with atypical GBS, particularly those with only motor signs (pure motor variant) and AMAN subtype, normal or even exaggerated reflexes might be observed throughout the disease course. 1
• This has been documented in pediatric cases, where a 10-year-old boy with GBS presented with preserved deep tendon jerks and extensor plantar response, successfully treated with IV immunoglobulin. 2

Critical Clinical Assessment

Temporal Profile

• GBS typically progresses to maximum disability within 2 weeks, with most patients reaching nadir within 7-14 days. 1, 3
• If progression occurs within 24 hours or after 4 weeks, alternative diagnoses should be strongly considered. 1

Preceding Infection History

• Approximately two-thirds of GBS patients report infection symptoms in the 6 weeks before onset, most commonly Campylobacter jejuni, cytomegalovirus, or Mycoplasma pneumoniae. 1, 3

Pain Assessment

• Severe pain (muscular, radicular, or neuropathic) is frequently reported in children with GBS and may lead to diagnostic delay. 1, 3
• Young children may present atypically with poorly localized pain, refusal to bear weight, or irritability. 1

Immediate Diagnostic Workup

Cerebrospinal Fluid Analysis

• Look for albuminocytologic dissociation (elevated protein with normal cell count), which supports GBS diagnosis. 4, 5
• Critical caveat: Protein may be normal in the first week of illness, so normal CSF does not exclude GBS. 4

Electrodiagnostic Studies

• Nerve conduction studies should demonstrate sensorimotor polyradiculoneuropathy with reduced conduction velocities, temporal dispersion, or conduction blocks in demyelinating forms. 4
• In AMAN variant, expect reduced or absent compound muscle action potentials (CMAPs) indicating axonal degeneration. 5

Neuroimaging

• MRI of the entire spine with and without contrast is mandatory to exclude spinal cord compression, transverse myelitis, or nerve root enhancement. 4

Urgent Management Priorities

Respiratory Monitoring

• Immediate hospitalization with intensive care capability is required because approximately 20% of GBS patients develop life-threatening respiratory failure. 4, 3
• Measure vital capacity, negative inspiratory force (NIF), and maximum inspiratory/expiratory pressures immediately using the "20/30/40 rule" to assess respiratory failure risk. 4

Autonomic Monitoring

• Monitor for dysautonomia including blood pressure and heart rate instability, which can be life-threatening. 1, 4

Immunomodulatory Treatment

• Intravenous immunoglobulin (IVIG) 2 g/kg over 5 days is the treatment of choice in children with GBS who have impaired ability to ambulate. 4, 3
• Treatment should be initiated urgently if clinical suspicion is high and imaging excludes structural lesions, without waiting for CSF or EMG confirmation. 4

Alternative Diagnoses to Exclude

Cerebral Palsy

• The flexor plantar response (normal Babinski) argues against upper motor neuron pathology like cerebral palsy, which would show extensor plantar response. 1, 6
• Cerebral palsy is non-progressive by definition, whereas this presentation describes acute ascending paralysis. 6

Spinal Muscular Atrophy

• SMA presents with hypotonia and areflexia/hyporeflexia, not brisk reflexes. 1, 5

Transverse Myelitis

• Would show bilateral upper motor neuron signs with extensor plantar responses, not flexor. 7

Critical Pitfalls to Avoid

• Do not dismiss GBS based on preserved or brisk reflexes alone, as this occurs in the AMAN variant. 1, 2
• Do not delay treatment waiting for CSF protein elevation, as it may be normal in the first week. 4
• Do not underestimate respiratory risk—any child with suspected GBS requires immediate hospitalization with respiratory monitoring capability. 3

Prognosis

The prognosis for full functional recovery in childhood GBS is excellent, with most children achieving complete recovery. 3