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Chapter Summary
• Context: Primary diseases of the vertebral column and intrinsic neurological disorders frequently share overlapping clinical presentations, including motor weakness, sensory disturbances, gait impairment, sphincter dysfunction, and axial or neuropathic limb pain. Because degenerative spine changes on MRI (disc bulging, facet arthropathy, canal narrowing) are widespread in the asymptomatic general population, discovering a structural vertebral abnormality in a patient with an underlying primary neurological disease can easily lead to diagnostic errors, delayed medical therapy, or unwarranted spinal surgery. This chapter structures the differential diagnosis between compressive spinal pathologies (cervical spondylotic myelopathy, compressive radiculopathy, lumbar spinal stenosis) and major non-compressive neurological diseases. It covers upper and lower motor neuron diseases (Amyotrophic Lateral Sclerosis [ALS]), central demyelinating and inflammatory disorders (Multiple Sclerosis [MS], Neuromyelitis Optica Spectrum Disorder [NMOSD], transverse myelitis), movement disorders (Parkinson disease, normal pressure hydrocephalus [NPH]), metabolic/toxic myelopathies (subacute combined degeneration from vitamin B12/copper deficiency), acute/chronic immune-mediated neuropathies (Guillain-Barré Syndrome [GBS], Chronic Inflammatory Demyelinating Polyradiculoneuropathy [CIDP]), and vascular malformations (dural arteriovenous fistulas). Synthesizing clinical history, cranial nerve examination, upper vs. lower motor neuron signs, cerebrospinal fluid analysis, neurophysiology, and targeted neuroimaging is essential for avoiding misdiagnosis and ensuring appropriate medical or surgical care.
• Chapter Objective: To present the clinical and neurological differential diagnosis between structural spinal disorders and primary neurological diseases. The reader should be able to differentiate motor neuron diseases (ALS) from cervical spondylotic myelopathy; identify demyelinating, inflammatory, and metabolic myelopathies mimicking spinal compression; distinguish movement disorders and normal pressure hydrocephalus from neurogenic claudication and myelopathic gait; and utilize electromyography, CSF analysis, and advanced neuroimaging to establish accurate, timely diagnoses.
• Clinical Reasoning and the "Double Trap" of NeuroimagingDiagnostic evaluation begins by distinguishing structural compressive myelopathy/radiculopathy from intrinsic central or peripheral neurological disorders. The presence of MRI canal stenosis in a patient with progressive neurological decline is not proof of compressive etiology. Clinicians must actively search for signs inconsistent with pure spinal compression: cranial nerve involvement, dysarthria, dysphagia, tongue fasciculations, cognitive decline, early prominent ataxia out of proportion to weakness, and widespread lower motor neuron denervation across non-contiguous cranial, cervical, thoracic, and lumbosacral segments.
• Motor Neuron Disease: Amyotrophic Lateral Sclerosis (ALS) vs. MyelopathyAmyotrophic lateral sclerosis (ALS) frequently mimics cervical spondylotic myelopathy (CSM) because both present with progressive upper extremity weakness, spasticity, and hyperreflexia. Crucial differentiating features of ALS include: 1) Simultaneous upper and lower motor neuron signs within the same limb; 2) Absence of sensory deficits (intact pinprick, light touch, and vibration); 3) Bulbar involvement (tongue atrophy, fasciculations, dysarthria, dysphagia); 4) Split-hand syndrome (preferential atrophy of thenar muscles and first dorsal interosseous with relative sparing of hypothenar muscles); and 5) Electromyography demonstrating active denervation (fibrillations, positive sharp waves) and chronic reinnervation in three or more anatomical regions (bulbar, cervical, thoracic, lumbosacral) with normal sensory nerve conduction.
• Demyelinating, Inflammatory, and Metabolic MyelopathiesMultiple sclerosis (MS) and Neuromyelitis Optica Spectrum Disorder (NMOSD) present with acute or subacute myelopathy (Lhermitte sign, optic neuritis, area postrema syndrome with intractable hiccups/vomiting). Spinal MRI in MS shows peripheral, short-segment (<2 vertebral segments), wedge-shaped posterolateral T2 hyperintensities; NMOSD shows longitudinally extensive transverse myelitis (LETM, >=3 contiguous vertebral bodies) with central cord involvement and positive serum Aquaporin-4 (AQP4-IgG) antibodies. Subacute Combined Degeneration (vitamin B12 deficiency) and copper deficiency produce symmetric dorsal and lateral column dysfunction (gait ataxia, loss of proprioception/vibration, spastic paraparesis) with characteristic inverted "V" sign T2 hyperintensity in the posterior columns.
• Movement Disorders, NPH, and PolyneuropathiesParkinson disease and Normal Pressure Hydrocephalus (NPH) cause gait disturbances easily confused with cervical myelopathy or lumbar spinal stenosis. Parkinsonism features resting tremor, cogwheel rigidity, bradykinesia, and a shuffling festinating gait. NPH presents with Adams-Hakim triad: magnetic "glued-to-the-floor" gait ataxia, cognitive decline, and urinary incontinence, with ventriculomegaly on brain CT/MRI. Guillain-Barré Syndrome (GBS) presents with acute ascending flaccid quadriparesis, hyporeflexia/areflexia, and albuminocytological dissociation on lumbar puncture. Spinal Dural Arteriovenous Fistulas (SDAVF) produce progressive slowly ascending lower extremity paraparesis and sphincter dysfunction in older males, appearing on T2 MRI as extensive cord edema and serpentine perimedullary flow voids.
• Clinical Application: In clinical practice, recognizing non-compressive neurological features prevents catastrophic surgical misadventures. In a patient referred for decompressive cervical laminectomy due to hyperreflexia and hand clumsiness, examining the cranial nerves and tongue for fasciculations and obtaining full-body needle EMG rules out ALS before irreversible cervical surgery is mistakenly performed. In a young adult presenting with acute paraparesis and a focal thoracic disc bulge, brain MRI and CSF analysis for oligoclonal bands and Aquaporin-4 antibodies distinguish multiple sclerosis or NMOSD from surgical disc herniation. In an elderly patient with bilateral leg weakness and MRI lumbar stenosis, testing for resting rigidity, assessing cognitive status, and examining for magnetic gait prevent unnecessary lumbosacral decompression for unrecognized Parkinson disease or NPH. When extensive thoracic cord T2 edema with perimedullary serpentine flow voids is noted, perform spinal digital subtraction angiography (DSA) to diagnose and embolize a spinal dural AV fistula.
