Validity and Responsiveness of Balance Measurements Using Posturography in Patients With Immune-Mediated Neuropathies

Abstract

Background and aims: Validated objective measures for balance in immune mediated neuropathies are lacking. In this study, we investigated the clinimetric properties of posturography using a force platform, a quantitative assessment of postural control.

Methods: We assessed patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and IgM-related polyneuropathy (IgM-PNP) using sway parameters (path, area and amplitude) measured at multiple time points. Validity was investigated by assessing differences in sway path between patients with and without reported balance symptoms and by assessing correlations of sway path with (established) impairment measures related to balance, disability and quality of life (QoL). Responsiveness was assessed by means of an anchor-based approach, using a patient anchor and two disability scales.

Results: We included 52 CIDP and 13 IgM-PNP patients. In CIDP, sway path was 25% longer in patients reporting balance symptoms relative to patients without balance symptoms (p = 0.03). There was excellent reliability between consecutive measurements in both CIDP and IgM-PNP. Moderate to good correlations were observed between sway path and an ataxia scale (CIDP: Spearman's ρ = 0.46, 95% CI: 0.2-0.69; IgM-PNP: Spearman's ρ = 0.72, 95% CI: 0.28-0.96) while correlations with related disability measures and QoL were poor. Changes in sway parameters over time were not consistently associated with changes in other outcome measures.

Interpretation: Posturography measurements showed poor validity and responsiveness. Therefore, despite excellent reliability, using a force platform in clinical practice or trials for immune-mediated neuropathies cannot be recommended.

Keywords: CIDP; IgM‐related polyneuropathy; balance; posturography; responsiveness; validity.

FIGURE 1

Conceptual framework for the construct of balance in patients with CIDP and IgM‐related polyneuropathy. Expected positive correlations between scores are represented by green arrows, expected negative correlations between scores are represented by red arrows. Ataxia 1 reflects an item assessing gait. Ataxia 2–5 reflects items assessing stance. Ataxia SS, ataxia sum score; CIDP, chronic inflammatory demyelinating polyneuropathy; EQ‐5D, EuroQol 5D, quality of life; HADS, Hospital Anxiety and Depression Scale; INCAT‐DS‐LE, Inflammatory Neuropathy Cause and Treatment Disability Score, lower extremities; mISS‐LE, modified Inflammatory Neuropathy Cause and Treatment Sensory Score, lower extremities; MRC‐SS‐LE, Medical Research Council sum score, lower extremities; RODS, Rasch‐built overall disability scale; TUG, timed up and go.

FIGURE 2

Distributions of disability and impairment measure scores. Disability and impairment scores in patients with CIDP and patients with IgM‐related polyneuropathy at first visit. Higher scores on the mISS, ataxia SS, INCAT‐DS and TUG indicate more severe impairment/disability. Lower scores on the MRC‐SS indicate more severe disability/impairment. Ataxia SS, ataxia sum score; CIDP, chronic inflammatory demyelinating polyneuropathy; IgM‐PNP, IgM‐related polyneuropathy; INCAT‐DS, Inflammatory Neuropathy Cause and Treatment Disability Score; I‐RODS, inflammatory Rasch‐built overall disability scale; mISS‐LE, modified Inflammatory Neuropathy Cause and Treatment Sensory Score; MRC‐SS, Medical Research Council sum score; TUG, timed up and go.

FIGURE 3

Sway path differences between patients with and without balance symptoms Log10 Sway path (mm) in the FAEO stance condition for patients with and without self‐reported balance symptoms, CIDP and IgM‐related polyneuropathy separately. Sway path is the total trajectory travelled by the CoP in millimetres, with increased sway path suggesting increased balance impairment. CIDP, chronic inflammatory demyelinating polyneuropathy; CoP, center of pressure; FAEO, feet apart eyes open; IgM‐PNP, IgM‐related polyneuropathy.

FIGURE 4

Sway path correlations with other outcome measures. (a) Correlations of sway path in the FAEO stance condition with other outcome measures, for patients with CIDP. (b) Correlations of sway path in the FAEO stance condition with other outcome measures, for patients with IgM‐related polyneuropathy. The first column represents correlations of sway path FAEO with other outcome measures, for example, in CIDP, sway path FAEO showed correlation of −0.34 with MRC‐LE. Only correlations with 95% confidence interval excluding 0 are shown. Ataxia SS, ataxia sum score; CIDP, chronic inflammatory demyelinating polyneuropathy; EQ‐5D, EuroQol 5D thermometer of quality of life; FAEO, feet apart eyes open; HADS, Hospital Anxiety and Depression Scale; I‐RODS, inflammatory Rasch‐built overall disability scale; INCAT‐DS‐LE, Inflammatory Neuropathy Cause and Treatment Disability Score, lower extremities; mISS LE, modified Inflammatory Neuropathy Cause and Treatment Sensory Score, lower extremities; MRC‐SS LE, Medical Research Council sum score, lower extremities; TUG, timed up and go.

FIGURE 5

Responsiveness in patients with CIDP. Distribution of sway path changes (mm) in FAEO stance condition (a) based on changes in leg disability represented by INCAT‐DS‐LE; (b) based on PGIC; (c) based on changes in I‐RODS (centile) equal or larger than the MCID of four points. ‘*’ represents a statistically significant difference. CIDP, chronic inflammatory demyelinating polyneuropathy; FAEO, feet apart eyes open; I‐RODS, inflammatory Rasch‐Built Overall Disability Scale; INCAT‐DS‐LE, INCAT disability score, lower extremities; MCID, minimal clinical important difference; PGIC, patient global impression of change.