Pure autonomic failure and the differential diagnosis of autonomic peripheral neuropathies

An overview on pure autonomic failure

Pure autonomic failure (PAF) is a neurodegenerative disease affecting the sympathetic component of the autonomic nervous system and presenting as orthostatic hypotension (OH). It is a rare, sporadic disease of adults. Although OH is the primary symptom, the autonomic dysfunction may be more generalised, leading to genitourinary and intestinal dysfunction and sweating disorders. Autonomic symptoms in PAF may be similar to those observed in other autonomic neuropathies that need to be ruled out. PAF belongs to the group of α synucleinopathies and is characterised by predominant peripheral deposition of α-synuclein in autonomic ganglia and nerves. However, in a significant number of cases, PAF may convert into another synucleinopathy with central nervous system involvement with varying prognosis: Parkinson's disease (PD), multiple system atrophy (MSA), or dementia with Lewy bodies (DLB). The clinical features, the main differential diagnoses, the risk factors for "phenoconversion" to another synucleinopathy as well as an overview of treatment will be discussed.

Small fiber neuropathy

Small fiber neuropathy (SFN) is a peripheral nervous system disease due to affection of A-delta or C-fibers in a proximal, distal, or diffuse distribution. Selective SFN (without large fiber affection) manifests with pain, sensory disturbances, or autonomic dysfunction. Though uniform diagnostic criteria are unavailable, most of them request typical clinical features and reduced intra-epidermal nerve fiber density on proximal or distal skin biopsy. Little consensus has been reached about the treatment of SFN, why this narrative review aims at summarizing and discussing treatment options for SFN. Treatment of SFN can be classified as symptomatic, pathophysiologic, or causal. Prerequisites for treating SFN are an established diagnosis, knowledge about the symptoms and signs, and the etiology. Pain usually responds to oral/intravenous pain killers, antidepressants, anti-seizure drugs, or topical, transdermal specifications. Some of the autonomic disturbances respond favorably to symptomatic treatment. SFN related to Fabry disease or hATTR are accessible to pathogenesis-related therapy. Immune-mediated SFN responds to immunosuppression or immune-modulation. Several of the secondary SFNs respond to causal treatment of the underlying disorder. In conclusion, treatment of SFN relies on a multimodal concept and includes causative, pathophysiologic, and symptomatic measures. It strongly depends on the clinical presentation, diagnosis, and etiology, why it is crucial before initiation of treatment to fix the diagnosis and etiology. Due to the heterogeneous clinical presentation and multi-causality, treatment of SFN should be individualized with the goal of controlling the underlying cause, alleviating pain, and optimizing functionality.