How Common Is Autonomic Neuropathy or Is It A Rare Disease?
Autonomic neuropathy is a collection of syndromes and diseases that affect the autonomic nervous system, involving either the sympathetic, or parasympathetic nervous system or even both. The autonomic nervous system has various functions in the body and the symptoms can either be subclinical or clinical depending on the disability they are causing. Autonomic neuropathy can be classified either as hereditary or acquired and acquired can further be divided into primary or secondary. All hereditary autonomic neuropathies are quite rare, which include familial amyloid polyneuropathy, hereditary sensory autonomic neuropathies, Fabry disease, and porphyrias. Acquired autonomic neuropathies are more common than inherited diseases.(1)
The primary form of acquired autonomic neuropathy is idiopathic in nature and has an autonomic neuropathy as a characteristic feature of the disease process. The secondary form of autonomic neuropathy is associated with some identifiable cause, as in the case of nutritional deficiency that may lead to autonomic neuropathy. Primary acquired autonomic neuropathies include pandysautonomia, idiopathic distal small fiber neuropathy, Holmes Adie syndrome, and Ross syndrome, chronic idiopathic anhidrosis, amyloid neuropathy, and postural orthostatic tachycardia syndrome.(1)
The secondary acquired autonomic neuropathies caused due to metabolic abnormalities include diabetes mellitus leading to diabetic neuropathy, uremic neuropathy, hepatic disease-related neuropathy, vitamin deficiency, and nutrition-related neuropathy, and toxic and drug-induced autonomic neuropathy. Alcohol is also associated with autonomic neuropathy. Infections leading to autonomic neuropathy include Lyme disease, HIV infection, Chagas disease, botulism, diphtheria, and leprosy. Autoimmune disorders that may lead to autonomic neuropathy include celiac disease, Sjogren’s syndrome, rheumatoid arthritis, systemic lupus erythematosus, Guillain Barre Syndrome, Lambert Eaton myasthenic syndrome, paraneoplastic autonomic neuropathy, and inflammatory bowel disease.(1)
Diabetic Autonomic Neuropathy
Diabetic neuropathy is the most common cause of neuropathy around the world. It can involve sensory, motor or autonomic nerves and can often coexist with these conditions. Diabetic neuropathy can either be focal/multifocal or generalized symmetric neuropathy and diabetic autonomic neuropathy is mostly classified under generalized symmetric neuropathy. In the past, it was mistakenly considered as a rare event; however, indeed it is a serious and an underestimated complication of diabetes. It is related to increased morbidity and mortality in diabetic patients. Since initially diabetic autonomic neuropathy is asymptomatic; it leads to delay in early diagnosis and treatment. Subclinical diabetic autonomic neuropathy can start as early as a year of diagnosis of type 2 diabetes mellitus and within 2 years in type 1 diabetes mellitus.(2)
Cardiovascular autonomic neuropathy is the most common manifestation of diabetic autonomic neuropathy. It is associated with increased mortality owing to its life-threatening complications that include arrhythmias, silent myocardial ischemia, and sudden death. There are various warning signs that can be used to detect cardiovascular autonomic neuropathy in the first years of diabetes and these include, reduced heart rate variability during a deep breath, QT interval prolongation, followed by resting tachycardia, impaired exercise tolerance and decreased baroreflex sensitivity leading to abnormal blood pressure and orthostatic hypotension.(2)
Other presenting signs and symptoms of diabetic autonomic neuropathy include increased chances of sleep apnea along with other comorbidities such as lung microvascular complications, endocrine impairments, obesity, and hypertension. Gastrointestinal symptoms, such as gastroparesis (nausea, vomiting, early satiety, bloating, postprandial fullness, abdominal pain), esophageal dysmotility, constipation, diarrhea, fecal incontinence, gall bladder atony. Gastric dysmotility can lead to an imbalance in acute glycemic control leading to delay in glucose absorption. Genitourinary dysfunction can lead to impaired bladder sensation, increased urinary retention, dysuria, nocturia, incomplete bladder emptying, urgency, overflow incontinence. Lower urinary tract symptoms predispose patients to recurrent urinary tract symptoms and predictive of long term development of renal failure. Sexual dysfunction leads to erectile dysfunction, retrograde ejaculation and decreased sexual desire in females, dyspareunia or inadequate lubrication. Sudomotor function abnormality leads to sweat gland denervation resulting in skin dryness. Pupillomotor function abnormality leads to the progressively decreased diameter of pupil at rest and disturbance in light reflex accommodation.(2)
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