[Autoimmune autonomic ganglionopathy: a case series of six patients and literature review]

The role of the laboratory in the expanding field of neuroimmunology: Autoantibodies to neural targets

Accelerated identification of autoantibodies associated with previously idiopathic neurological disease has provided insights into disease mechanisms, enhanced understanding of neurological function, and opportunities for improved therapeutic interventions. The role of the laboratory in the expanding field of neuroimmunology is critical as specific autoantibody identification provides guidance to clinicians in diagnosis, prognosis, tumor search strategies, and therapeutic interventions. The number of specific autoantibodies identified continues to increase and newer testing strategies increase efficiencies in the laboratory and availability to clinicians. The need for broadly targeted efficient testing is underscored by the variability in clinical presentation and tumor associations attributable to a specific autoantibody, and conversely the various autoantibody specificities that can be the cause of a given clinical presentation. While many of the antineural antibodies were first recognized in the setting of neoplastic disease, idiopathic autoimmune neurological disease in the absence of underlying tumor is increasingly recognized. Appropriation of therapeutic modalities used to treat autoimmune disease to treat these autoantibody mediated neurological diseases has improved patient outcomes. Interaction between clinicians and laboratorians is critical to our understanding of these diseases and optimization of the clinical benefits of our increasing knowledge in neuroimmunology.

Ganglionic Antibody Level as a Predictor of Severity of Autonomic Failure

OBJECTIVE

To assess antibody level as a test of autonomic failure (AF) associated with ganglionic nicotinic acetylcholine receptor antibody (AChR-Ab) autoimmunity.

PATIENTS AND METHODS

We searched the Mayo Clinic laboratory database of 926 ganglionic AChR-Ab-seropositive patients seen at our institution between October 1, 1997, and April 1, 2015, for initial level of 0.05 nmol/L or higher and contemporaneous autonomic reflex screen (standardized evaluation of adrenergic, cardiovagal, and sudomotor functions) from which Composite Autonomic Scoring Scale (CASS) scores could be calculated.

RESULTS

Of 289 patients who met inclusion criteria, 163 (56.4%) were women, median age was 54 years (range, 10-87 years), median antibody level was 0.11 nmol/L (range, 0.05-22.10 nmol/L), and median CASS total score was 2.0 (range, 0-10). Using receiver operating characteristic curve analysis, a level above 0.40 nmol/L predicted severe AF (CASS score, ≥7) with 92% specificity and 56% sensitivity. For at least moderate AF (CASS score ≥4 and anhidrosis ≥25%), a level of at least 0.20 nmol/L had 80% specificity and 59% sensitivity. Levels below 0.20 nmol/L were not predictive of the presence or absence of AF. For predicting orthostatic hypotension, ganglionic AChR-Ab level had excellent specificity above 0.4 nmol/L but lacked sensitivity. Autoantibodies to additional targets were present in 61 patients (21.1%).

CONCLUSION

Ganglionic AChR-Ab level of at least 0.40 nmol/L is a moderately sensitive and highly specific marker for severe AF, as is a level of at least 0.20 nmol/L for moderate AF if CASS score is coupled with anhidrosis of 25% or more, among patients with suspected ganglionic AChR-Ab autoimmune autonomic ganglionopathy. Antibody levels of less than 0.20 nmol/L have little clinical importance in the absence of clinical AF.