Sensory neuronopathy, also known as sensory ganglionopathy, is a rare subgroup of peripheral nervous system diseases with specific characteristics, such as the primary and selective destruction of the dorsal root ganglia (DRG) neuron in the spinal cord and the trigeminal ganglia neuron in the skull.
It has a typical clinical presentation, with sensory deficits that are not dependent on length and patients often report a lack of coordination of muscle movements. There are several proposed mechanisms for the pathophysiology of the condition. The diagnosis is guided by the presenting symptoms and confirmed with diagnostic tests to differentiate from other related conditions.
History
In 1948, sensory neuronopathy was described for the first time by Denny-Brown, who observed two patients with the condition concurrently with bronchial carcinoma. Symptoms were noted in the arms, legs, face and tongue of the patients and post-mortem analysis revealed significant degeneration of the DRG neurons.
The involvement of the dorsal root ganglia neurons has since been further studied by other researchers. As a result of this, several mechanisms as to the pathology of the condition have been proposed.
Pathophysiology
The most common cause of sensory neuronopathy is thought to be immune-mediated damage to the DRG neurons. This often affects both the central and peripheral “T-shaped” neurons and their projections, rather than specific sections that are evident and many other polyneuropathies. Other possible causes of the condition include genetic susceptibility, adverse drug reactions and infections.
The damage to the neurons has been linked to abnormal blood supply via the capillaries, leading to the entry of inflammatory cells, proteins and other toxins into the neurons. Some research has also suggested that CD8 T lymphocytes and some antibodies may be involved in the pathology of the condition.
Symptoms
The classic symptoms of sensory neuronopathy are multifocal, often linked to ataxia and extending to both proximal and distal regions of the body. These may include lack of voluntary muscle movement coordination and abnormal gait. Other symptoms may include:
- Areflexia
- Pseudoathetotic hand movements
- Allodynia
- Tonic pupils
- Orthostatic hypotension
- Gastrointestinal effects
- Erectile dysfunction
- Memory deficits
- Behavioral changes
The presentation and severity of symptoms depend greatly on the type of fibers involved in the pathology of the condition for the individual. It may have an impact of all senses modalities, including pain, temperature, position and vibration.
Diagnosis
Sensory neuronopathy is characterized by unique symptoms that give it a distinctive clinical picture, which aids in the diagnosis of the condition. Initially, reported symptoms can give a good indication as to the involvement of sensory neuronopathy. Relevant examination and analyses can then be undertaken to confirm the diagnosis.
- Nerve conduction studies are the most useful tool, as they show the changes in the sensory action that may be indicative of the condition. In particular, asymmetric responses are typically seen in patients with sensory neuronopathy.
- Magnetic resonance imaging (MRI) can help in the diagnostic process to identify patients with subtle damage to the DRG neurons.
- Pathological analyses can also be used to investigate the condition further and help reach the correct diagnosis.
Related Conditions
People that suffer from sensory neuronopathy are more likely to be affected by other autoimmune diseases. A differential diagnosis is important to distinguish sensory neuronopathy from other related conditions, such as sensory and ataxic neuropathy. These conditions may include Sjögren’s Syndrome, autoimmune hepatitis and celiac disease.
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