Assessment and evaluation of hereditary sensory and autonomic neuropathies with autonomic and neurophysiological examinations

The five different types of the rare hereditary sensory and autonomic neuropathies (HSAN) are classified by their mode of inheritance, pathology, natural history, biochemical, neurophysiologic and autonomic abnormalities. Clinically, the different types of HSANs can be identified by a detailed history and examination and 'bedside' tests of sympathetic or parasympathetic function such as active standing, metronomic breathing or the Valsalva maneuver, sensory and motor nerve conduction studies, quantitative sensory testing of thermal and vibratory perception, and the analysis of sudomotor function by recordings of the sympathetic skin response (SSR) or the sweat output during quantitative sudomotor axon reflex testing (QSART). The slowly progressive, symmetrical HSAN type I manifests between the second and fourth decade with ulcers or mutilations of the lower extremities, low normal sensory and motor nerve conduction velocities, but abnormal warm, cold and heat pain perception and distal anhidrosis. In HSAN type II, symptoms occur already in infancy, trophic alterations affect fingers and toes. There are acral anhidrosis and various autonomic dysfunctions such as tonic pupils, eating and swallowing difficulties, constipation, episodic fever, profound hypotonia and episodes of apnea. Sensory perception is severely impaired and accounts for elevated vibratory but also thermal perception thresholds. Sensory nerve conduction is highly abnormal while motor nerve conduction studies are almost normal. Type III, the autosomal recessive familial dysautonomia (FD), is the most common of the HSANs. FD is characterized by pronounced autonomic, primarily sympathetic dysregulation with severe orthostatic hypotension, repeated episodes of autonomic crises with excessive arterial hypertension, profuse sweating, skin blotching, puffy hands and behavioral abnormalities. FD manifests only in children of Ashkenazi Jewish ancestry. Cardinal findings are diminished deep tendon reflexes, absence of overflow tears, absence of fungiform papillae of the tongue and of axon flare response following intradermal histamine injection. Thermal and vibratory testing show pronounced impairment of temperature and pain but also of vibratory perception. Children with HSAN IV, 'congenital insensitivity to pain with anhidrosis', experience repeated episodes of high fevers during high environmental temperature due to anhidrosis. The anhidrosis of the hyperkeratotic skin accounts for absence of the SSR or lack of sweat output during QSART. The patients' insensitivity to superficial as well as deep, visceral pain can be demonstrated e. g. by quantitative heat pain testing. Patients develop severe mutilations e. g. of the tip of their tongue, they might have severe burn injuries and multiple, unnoticed fractures with neuropathic joints. Children with the very rare HSAN type V respond normally to tactile, vibratory or thermal stimuli, but have a selective loss of pain perception with otherwise normal neurological examination. Painful stimuli reveal no signs of discomfort.