Peripheral neuropathy –
Peripheral neuropathy cases are increasing at a high rate. Older people and patients suffering from diseases like diabetes are at high risk.
It is essential to understand how peripheral neuropathy develops and what its underlying cause is. After this information, the doctor can treat the patient to improve the symptoms of the patient.
What is peripheral neuropathy?
It is a group of disorders that can happen due to injury to the peripheral nervous system.
The peripheral nervous system is part of the nervous system, which includes all neural structures lying outside the pial membrane of the spinal cord and brainstem except the optic nerve and olfactory bulb.
Functions of the peripheral nervous system-
Peripheral nerves are composed of sensory, motor, and autonomic elements.
These nerves can be subdivided into three classes: Large myelinated, small myelinated, and small unmyelinated.
Large diameter sensory fibers conduct proprioception (which means it allows the body to know the position of your body and helps to maintain the balance of the body) and vibratory sensation to the brain.
Small-diameter myelinated and unmyelinated fibers transmit pain and temperature sensation.
Peripheral neuropathy Types-
1) Acquired peripheral polyneuropathy –
Diabetes, cryptogenic sensory peripheral neuropathy, and chemotherapy-induced peripheral neuropathy.
2) Genetic peripheral polyneuropathy –
Charcot-Marie-Tooth disease
3) Mononeuritis Multiplex-
Vasculitis
4) Polyradiculopathy
Acute or chronic inflammatory demyelinating polyradiculoneuropathy, diabetic radiculoplexus neuropathy
5) Sensory Neuropathy-
Sjogren syndrome, para-neoplastic, idiopathic
7 steps to determine the type of peripheral neuropathy
1) Identify the involved system-
First, identify if the patient’s signs and symptoms are due to motor, sensory, or autonomic, or if all three are involved.
- Neuromuscular junction – If the patient complains of weakness only without any involvement of sensory or autonomic dysfunction, then it points towards the involvement of the neuromuscular junction.
- Autonomic nervous systems- If the autonomic nervous system is involved, then patients complain of fainting spells or orthostatic lightheadedness, heat intolerance, bowel, bladder, or sexual dysfunction.
2) Identifying weakness pattern-
Important questions to be answered first are-
- Weakness is limited to the distal extremity or both proximal and distal in nature?
- Weakness is focal and asymmetric, or is it symmetric?
Symmetric proximal and distal weakness is seen in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy.
If the patient does not have any signs or symptoms related to the sensory system, then such weakness can be due to motor neuron disease (eg, amyotrophic lateral sclerosis [ALS]).
ALS patients can show signs and symptoms such as neck extensor weakness (neck drop), tongue and pharyngeal weakness (dysarthria and dysphagia), and breathing difficulties.
The above-mentioned signs and symptoms can also be seen in diseases like myasthenia Gravis, Lambert-Eaton myasthenic syndrome (LEMS).
3) Sensory involvement in peripheral neuropathy-
Patient may have loss of sensation (numbness), altered sensation to touch, or may feel uncomfortable spontaneous sensations such as tingling, burning, or pain.
Small fiber neuropathy
The patient can complain of loss of pain and temperature sensation.
Other senses like vibration, position, muscle power, and deep tendon reflexes are preserved.
Eg – Diabetes mellitus.
4) Upper motor neuron involvement-
In upper motor neuron involvement, the distal muscle group is affected more severely than the proximal muscles.
Spasticity may present later with disease progression.
In corticobulbar involvement, patients usually complain of weakness in the lower face and tongue.
Upper facial, pharyngeal, and jaw muscles are typically not affected.
Most commonly, it is seen in vitamin B12 deficiency. Other causes include HIV infection, copper deficiency, and severe hepatic disease.
5) Chronology of peripheral neuropathy –
It is important to determine how and when the signs and symptoms developed.
Acute – Signs and symptoms take a few days to 4 weeks.
Subacute- 4 to 8 weeks
Chronic- More than 8 weeks
Acute and subacute presentation is seen in GBS, vasculitis.
6) Medical History of the patient
Always ask about the medical history of the patient, such as Diabetes, SLE, any surgeries (gastric bypass and nutritional neuropathies), medicines (toxic neuropathy), and dentures ( fixatives contain zinc that can lead to copper deficiency).
7) Hereditary peripheral neuropathy-
Slowly progressive distal weakness can be seen in Charcot-Marie-Tooth disease.
Peripheral neuropathy diagnosis –
Electrodiagnostic studies-
These studies include-
- Nerve conduction study (NCS)
- Needle electromyocardiography (EMG)
These tests can help to confirm whether the neuropathic disorder is a mononeuropathy, multiple mononeuropathy, radiculopathy, plexopathy, or generalized polyneuropathy.
These tests also help to understand whether the neuropathy involves only sensory fibers, motor fibers, autonomic fibers, or a combination of these fibers.
Laboratory test for peripheral neuropathy
Routine blood tests include complete blood count, liver function test, kidney function test, serum electrolytes, fasting blood glucose, HbA1c, Thyroid function test, urine test, Vitamin B12, folate, Erythrocyte sedimentation rate (ESR), Rheumatoid factor, Anti nuclear antibodies, Serum Protein electrophoresis for multiple myeloma or other serum protein disorder, immuno electrophoresis and urine for bence jones protein.
A skeletal survey should be performed in patients with acquired demyelinating neuropathies and M spikes to look for osteosclerotic or lytic lesions.
A bone marrow biopsy should be done in patients with monoclonal gammopathy.
An oral glucose tolerance test is indicated in patients with painful sensory neuropathy, even if fasting blood sugar and HbA1c are normal.
If the patient is suffering from a mononeuropathy multiplex pattern, then the following tests should be done:
Antineutrophil cytoplasmic antibodies (ANCA), cryoglobulins, hepatitis serology, western blot for Lyme disease, and HIV.
If GBS or CIDP is suspected, then a lumbar puncture is indicated to look for elevated CSF protein.
CSF pleocytosis is usually absent in idiopathic cases of GBS or CIDP. These cells are usually present in HIV infection, Lyme disease, and sarcoidosis
Some patients with GBS and CIDP have abnormal liver function tests. In these types of cases, it is also important to check hepatitis B and C, HIV, EBV, and CMV infection.
In patients with severe sensory ataxia, a sensory ganglionopathy or neuronopathy should be considered. The most common cause is Sjogren syndrome, and hence it is important to inquire about dry eye and mouth in patients with sensory signs and symptoms. These patients should also be checked for antibodies to SS-A/RO and SS-B/La, along with ANA.
Nerve Biopsy
Nerve biopsy is now rarely used and should be performed only when the nerve conduction study (NCS) is abnormal.
The sural nerve is the most commonly biopsied nerve because it is a pure sensory nerve, and a biopsy will not result in loss of motor function.
Skin Biopsy in peripheral neuropathy –
It is used to diagnose small fiber neuropathy.
Punch biopsy of the skin of the lower extremity is done, and immunologic staining is performed to measure the density of small unmyelinated fibers.
A decrease in the density of the nerve fiber is seen in patients with small fiber neuropathy.
