Multimodal Biomarkers Quantify Recovery in Autoimmune Autonomic Ganglionopathy

Abstract

Objective The objective of this study was to evaluate patients with ganglionic acetylcholine receptor antibody (gAChR‐Ab) positive autoimmune autonomic ganglionopathy using a multimodal testing protocol to characterize their full clinical phenotype and explore biomarkers to quantify immunotherapy response. Methods We conducted a cohort study of 13 individuals (7 women, 21–69 years of age) with autonomic failure and gAChR‐Ab >100 pM identified between 2005 and 2019. From 2018, all patients were longitudinally assessed with cardiovascular, pupillary, urinary, sudomotor, lacrimal and salivary testing, and Composite Autonomic Symptom Score (COMPASS‐31) autonomic symptom questionnaires. The orthostatic intolerance ratio was calculated by dividing change in systolic blood pressure over time tolerated on head‐up tilt. Eleven patients received immunotherapy. Results At first assessment, all 13 patients had cardiovascular and pupillary impairments, 7 of 8 had postganglionic sudomotor dysfunction, 9 of 11 had urinary retention and xeropthalmia, and 6 of 8 had xerostomia. After immunotherapy, there were significant improvements in orthostatic intolerance ratio (33.3 [17.8–61.3] to 5.2 [1.4–8.2], p = 0.007), heart rate response to deep breathing (1.5 [0.0–3.3] to 4.5 [3.0–6.3], p = 0.02), pupillary constriction to light (12.0 [5.5–18.0] to 19.0 [10.6–23.8]%, p = 0.02), saliva production (0.01 [0.01–0.05] to 0.08 [0.02–0.20] g/min, p = 0.03), and COMPASS‐31 scores (52 to 17, p = 0.03). Orthostatic intolerance ratio correlated with autonomic symptoms at baseline (r = 0.841, p = 0.01) and following immunotherapy (r = 0.889, p = 0.02). Immunofluorescence analyses of skin samples from a patient 32 years after disease onset showed loss of nerve fibers supplying the dermal autonomic adnexa and epidermis, with clear improvements following immunotherapy. Interpretation Patients with autoimmune autonomic ganglionopathy demonstrated objective evidence of widespread sympathetic and parasympathetic autonomic failure, with significant improvements after immunotherapy. Quantitative autonomic biomarkers should be used to define initial deficits, guide therapeutic decisions, and document treatment response. ANN NEUROL 2021;89:753–768

A Flow Cytometric Assay to Detect Functional Ganglionic Acetylcholine Receptor Antibodies by Immunomodulation in Autoimmune Autonomic Ganglionopathy

“…These factors may explain the unexpected findings discussed above of a high proportion of gnACHR subunit specific antibody positivity in patients with SLE assessed by LIPS (9.4% ( 9 )), even without autonomic dysfunction., which was not seen in our immunomodulation assay. The RIA assay also displays great analytical sensitivity, but at the cost of specificity when the decision limit is low; the current decision limit for the gnACHR antibody RIA performed at Mayo Clinic (Rochester) is 20pM ( 25 ), although this test only starts being reasonably specific for clinically meaningful autonomic failure at 200pM, and very specific at levels above 400pM ( 8 ), which is further verified in a study by the Oxford group in which AAG patients, when seropositive for gnACHR antibodies, have levels that exceed 200pM ( 11 ).…”

“…To prevent data contamination by selection bias (i.e., identifying presumed AAG patients solely by our novel assay in order to circuitously prove our assay functions as intended), we obtained blinded samples from Oxford. The positive samples were recruited from a clinically well-characterized published cohort of AAG patients ( 11 ). Many of the patients were historical, without stored serum for analysis.…”

“…One hundred and ninety samples were assessed for gnACHR immunomodulation: Plasma and serum from one patient with seropositive AAG (established by RIA) was used to validate the novel flow cytometric assay, and this was then validated with two further seropositive samples obtained from the Nuffield Department of Clinical Neurosciences, Oxford. Nine other samples were also supplied by the Oxford group; a mixture of seropositive [full clinical characterization of these and other samples has recently been published by Koay et al ( 11 )] and seronegative samples that were blinded for gnACHR antibody status. RIA was performed as previously described, in brief, solubilized IMR-32 membranes containing gnACHR were complexed with 125 I-epibatidine prior to the addition of serum, then immunocomplexes were precipitated out.…”

“…Local patient samples were obtained between 2015-2016 from in- or outpatient services attached to the Royal Prince Alfred hospital, Sydney, on a convenience basis. Collection of samples submitted from Oxford occurred between 2005 – 2019 as previously described ( 11 ).…”

Towards more evidenced-based therapies for postural tachycardia syndrome and other updates on recent autonomic research

“…Prior studies evaluating response to treatment predominantly evaluated effects on cardiovascular and sudomotor function or results of autonomic reflex testing (Composite Autonomic Severity Score) with variable evidence of objective benefit, even though patients frequently report improved symptom burden. To document the extent of autonomic recovery after treatment of AAG, Koay et al recently published their work online [2] titled "Multimodal Biomarkers Quantify Recovery in Autoimmune Autonomic Ganglionopathy" in Annals of Neurology.…”