What are the differential diagnoses of quadriplegia?

Differential Diagnoses of Quadriplegia

The differential diagnosis of quadriplegia must be systematically organized by anatomical localization—CNS (brainstem and spinal cord), peripheral nervous system, neuromuscular junction, muscle, and metabolic/functional causes—with urgent imaging and laboratory evaluation to distinguish life-threatening conditions requiring immediate intervention.

Anatomical Framework for Differential Diagnosis

The key to diagnosing quadriplegia is determining the anatomical level of pathology through clinical examination, particularly reflexes, sensory level, and associated features 1.

Central Nervous System Causes

Spinal Cord Pathology:

• Inflammation or infection of the spinal cord including acute transverse myelitis, sarcoidosis, Sjögren syndrome, neuromyelitis optica, or myelin oligodendrocyte glycoprotein antibody-associated disorder 1
• Spinal cord compression from structural lesions, which requires urgent MRI evaluation 1
• Malignancy such as leptomeningeal metastases or neurolymphomatosis 1
• Vitamin deficiencies including subacute combined degeneration from vitamin B12 deficiency 1

Brainstem Pathology:

• Brainstem stroke, particularly midline ischemic lesions involving bilateral pyramidal tracts in the medulla or pons 1, 2
• Inflammation or infection of the brainstem from sarcoidosis, Sjögren syndrome, neuromyelitis optica, or myelin oligodendrocyte glycoprotein antibody-associated disorder 1
• Brainstem compression 1

Clinical Pitfall: Hyperreflexia, clonus, extensor plantar responses, or a sharp sensory level indicate CNS pathology rather than peripheral causes 1.

Peripheral Nervous System Causes

Guillain-Barré Syndrome (GBS):

• Classic presentation includes progressive bilateral weakness starting in legs, absent or decreased reflexes, and progression over days to 4 weeks 1
• Strongly supportive features include bilateral facial palsy, autonomic dysfunction, albuminocytologic dissociation in CSF (elevated protein with normal cell count), and preceding infection 1
• Features casting doubt on GBS diagnosis include marked asymmetry, bladder/bowel dysfunction at onset, sharp sensory level, hyperreflexia, fever at onset, or CSF pleocytosis >50 × 10⁶/L 1

Other Peripheral Neuropathies:

• Acute flaccid myelitis, particularly in children 1
• Neurosyphilis with tract-specific myelopathy 3

Muscle and Metabolic Causes

Metabolic and Electrolyte Disorders:

• Hypokalemia, thyrotoxic hypokalemic periodic paralysis, hypomagnesemia, or hypophosphataemia 1
• These typically present with preserved reflexes initially and respond rapidly to electrolyte correction 1

Primary Muscle Disorders:

• Inflammatory myositis 1
• Acute rhabdomyolysis 1
• Drug-induced toxic myopathy from colchicine, chloroquine, emetine, or statins 1
• Mitochondrial disease 1

Clinical Clue: Elevated creatine phosphokinase levels help distinguish myopathic from neurogenic causes 4.

Functional Causes

Conversion or Functional Disorder:

• Must be a diagnosis of exclusion after thorough workup 1
• Can present as functional quadriplegia even in patients with underlying rheumatologic conditions 5

Critical Diagnostic Algorithm

Step 1: Assess Reflexes and Upper Motor Neuron Signs

• Hyperreflexia/clonus/Babinski sign → CNS localization (spinal cord or brainstem) requiring urgent MRI 1
• Hyporeflexia/areflexia → Consider peripheral nerve (GBS), muscle, or metabolic causes 1

Step 2: Identify Red Flags for Specific Diagnoses

• Sensory level → Spinal cord pathology 1
• Bilateral facial palsy → GBS variant 1
• Bladder/bowel dysfunction at onset → Spinal cord lesion, not typical GBS 1
• Rapid progression <24 hours → Consider brainstem stroke, metabolic crisis, or alternative to GBS 1, 2
• Fever at onset → Infection, not typical GBS 1

Step 3: Obtain Urgent Investigations

• MRI of brain and entire spine is the preferred imaging modality for myelopathy evaluation 1
• Electrolytes including potassium, magnesium, phosphate 1, 4
• CSF analysis if peripheral neuropathy suspected (protein elevation with normal cell count supports GBS; pleocytosis >50 cells suggests alternative diagnosis) 1
• Creatine phosphokinase to evaluate for myopathy 4
• Electrodiagnostic studies to distinguish neuropathy from myopathy, though may be normal early in GBS 1

Step 4: Consider Treatable Causes First

• Spinal cord compression requiring surgical decompression 1
• Electrolyte abnormalities requiring immediate correction 1, 4
• GBS requiring immunotherapy (IVIG or plasma exchange) 1
• Neurosyphilis requiring penicillin therapy 3
• Vitamin deficiencies requiring supplementation 1, 4

Common Pitfalls to Avoid

• Do not assume GBS if hyperreflexia, sensory level, or early bladder dysfunction present—these suggest spinal cord pathology 1
• Do not delay MRI in patients with upper motor neuron signs, as spinal cord compression is a neurosurgical emergency 1
• Do not rule out GBS based on normal early CSF protein or electrophysiology, as these can be normal in the first week 1
• Do not overlook metabolic causes in patients with preserved reflexes and rapid onset, as these are immediately reversible 1, 4
• Do not miss brainstem stroke presenting as isolated quadriplegia—look for midline pontine or medullary lesions on MRI 2