Is dis-equilibrium (loss of balance) a contributing factor in patients presenting with standing ataxia, particularly those with a history of neurological disorders?

Disequilibrium and Standing Ataxia: Terminology and Clinical Distinction

Disequilibrium is not synonymous with standing ataxia, but rather represents a symptom or component that can manifest within ataxic presentations. The terms describe different aspects of balance dysfunction that require careful clinical distinction.

Defining the Terms

Disequilibrium refers specifically to a subjective sensation of imbalance or unsteadiness, often described as loss of balance control 1. It represents a symptom rather than a specific diagnosis and can arise from multiple etiologies including cerebellar, sensory, vestibular, or even frontal lobe pathology 1.

Standing ataxia (or truncal ataxia) describes the objective finding of difficulty maintaining posture and balance while standing, particularly prominent with cerebellar vermian pathology 2. This represents a specific motor examination finding rather than a subjective complaint 2.

Clinical Relationship Between the Two

• Disequilibrium frequently presents as a contributing symptom in patients with standing ataxia, particularly those with cerebellar degeneration 1, 2
• Patients with chronic disequilibrium due to sensory ataxia show loss of proprioception that is out of proportion to other sensory modalities 1
• In cerebellar ataxia specifically, disequilibrium manifests alongside truncal instability, dysmetria, and dysdiadochokinesia 2

Critical Distinguishing Features for Clinical Assessment

Cerebellar-origin disequilibrium/ataxia:

• Unsteadiness does not significantly worsen with eye closure (negative Romberg test) 2, 3
• Persists regardless of visual input 2, 4
• Associated with wide-based gait, dysmetria, dysarthria, and nystagmus 2

Sensory (proprioceptive) ataxia with disequilibrium:

• Symptoms worsen dramatically when visual input is removed (positive Romberg test) 3
• Results from dorsal column dysfunction affecting position sense 1, 3
• Patients rely heavily on vision to compensate for proprioceptive loss 3

Frontal lobe-origin disequilibrium:

• May mimic cerebellar syndrome but results from disturbance in cerebellar-frontal circuitries 5
• Characterized by loss of motor planning control leading to imbalance 5

Clinical Implications

• Disequilibrium in cerebellar ataxia appears to be a more influential cause of orthostatic intolerance than hemodynamic dysfunction alone 6
• Patients with disequilibrium are more likely to fail standing tolerance tests (46% vs 3% in those without disequilibrium, p<0.01) 6
• The presence of disequilibrium alongside ataxia indicates greater functional impairment and sitting intolerance in addition to standing problems 6

Common Pitfalls to Avoid

• Do not use the terms interchangeably: Disequilibrium is a symptom; standing ataxia is an examination finding 1, 2
• Do not assume all disequilibrium is cerebellar: Frontal lobe lesions can produce disequilibrium that mimics cerebellar dysfunction 5
• Do not skip the Romberg test: This distinguishes cerebellar from sensory causes, though it cannot be properly performed if unsteadiness is severe regardless of visual input 2, 3
• Do not overlook that disequilibrium and gait irregularity are separate, independent components of cerebellar ataxic gait 7