What are the differential diagnoses for sensory ataxia?

Differential Diagnoses for Sensory Ataxia

Sensory ataxia results from dysfunction of proprioceptive pathways affecting the dorsal root ganglia, dorsal columns of the spinal cord, or peripheral sensory nerves, and the differential diagnosis must systematically address each anatomical level of potential involvement. 1

Key Distinguishing Feature

• Sensory ataxia characteristically worsens with eye closure (positive Romberg test), as patients rely heavily on vision to compensate for lost proprioception—this is the critical feature distinguishing it from cerebellar ataxia. 1, 2, 3

Spinal Cord Pathology (Dorsal Column Involvement)

Compressive Lesions

• Compressive myelopathy from disc herniation, spinal stenosis, or tumor causing dorsal column compression 1, 2

Metabolic/Nutritional Causes

• Vitamin B12 deficiency (subacute combined degeneration) affecting dorsal columns 1, 2
• Copper deficiency causing myeloneuropathy with dorsal column involvement 1, 2

Infectious Causes

• Tabes dorsalis (neurosyphilis) causing dorsal column degeneration 1, 2

Inflammatory/Demyelinating Causes

• Inflammatory myelopathies affecting dorsal columns 1
• Neoplastic infiltration of the spinal cord 1

Peripheral Nerve and Dorsal Root Ganglion Pathology

Immune-Mediated Neuropathies

• Autoimmune sensory ataxic neuropathies (sensory neuronopathies/ganglionopathies) 1, 2
• Chronic idiopathic ataxic neuropathy presenting with profound proprioceptive loss, often associated with monoclonal or polyclonal gammopathy 4
• Paraneoplastic sensory neuronopathy associated with anti-Hu antibodies and malignancy 4

Hereditary Neuropathies

• Sensory/motor neuropathy with ataxia (SMNA) showing autosomal dominant inheritance 5
• Hereditary sensory neuropathies (HSN) with prominent ataxia 5
• Certain spinocerebellar ataxias (SCAs) with peripheral neuropathy component 1

Toxic Neuropathies

• Pyridoxine (vitamin B6) toxicity causing sensory neuronopathy 4
• Chemotherapy-induced neuropathy (e.g., doxorubicin, cisplatin) 4

Other Peripheral Causes

• Large fiber sensory neuropathy from various etiologies (diabetes, uremia, etc.) 6, 4
• Ataxic neuropathy affecting distal nerve endings 6

Mixed Central and Peripheral Syndromes

• Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS) combining both central cerebellar and peripheral sensory components 1
• Spinocerebellar ataxias with coexisting peripheral neuropathy 1

Diagnostic Algorithm

Step 1: Confirm Sensory Ataxia

• Verify positive Romberg test (dramatic worsening with eye closure) 1, 2, 3
• Document sensory loss, hyporeflexia, and preserved strength (distinguishes from cerebellar ataxia) 1, 3

Step 2: Localize the Lesion

• MRI cervical and thoracic spine without IV contrast to evaluate dorsal columns for compressive myelopathy, B12/copper deficiency, or tabes dorsalis 1, 2
• Add IV contrast if inflammatory, infectious, or neoplastic causes suspected 1, 2
• Look for spinal cord atrophy suggesting degenerative ataxia 1, 2

Step 3: Electrodiagnostic Testing

• Nerve conduction studies and EMG to document large fiber sensory neuropathy or dorsal root ganglion involvement 2, 6
• Absent sensory potentials with normal motor studies suggest sensory neuronopathy 4

Step 4: Laboratory Evaluation for Treatable Causes

• Vitamin B12 and methylmalonic acid levels 2
• Serum copper and ceruloplasmin 2
• Syphilis serology (RPR/VDRL and treponemal testing) 2
• Serum protein electrophoresis and immunofixation (check for paraproteinemia) 4
• Paraneoplastic antibody panel if subacute onset 4
• Consider genetic testing if family history present 5

Step 5: Consider Advanced Testing

• Targeted ultrasound may detect nerve size changes in some ataxic neuropathies (investigational) 1, 2
• Nerve biopsy showing severe loss of large myelinated fibers confirms sensory neuronopathy 4

Critical Pitfalls to Avoid

• Do not mistake sensory ataxia for cerebellar ataxia—the Romberg test is the key differentiator, as cerebellar ataxia does not significantly worsen with eye closure 1, 2, 3, 7
• Always investigate treatable causes first (B12, copper, neurosyphilis, compression) before concluding the condition is idiopathic 2
• Recognize that sensory ataxia originates from proprioceptive pathway damage, not cerebellar dysfunction 1, 2, 8
• In chronic progressive cases with gammopathy, consider chronic idiopathic ataxic neuropathy, which is typically resistant to immunotherapy despite potential immune mechanisms 4