Lower Extremity Mononeuropathy Flashcards
What is a mononeuropathy?
A mononeuropathy may result from pathology located anywhere along the course of the peripheral nerve, from the dorsal root ganglion through to the lumbosacral plexus and the terminal individual named nerves.
Dysfunction can lead to weakness, pain, or sensory deficits. These entities are a major source of neurological referral.
What are the causes of mononeuropathies?
Mononeuropathies can be thought of as compressive or idiopathic, or as sequelae of underlying systemic disease (e.g., diabetes, malignancy, infection, and inflammatory conditions).
Lumbosacral plexopathies
o Neuropathy involving the lumbosacral plexus. It can be caused by compressive, infectious, malignant, and inflammatory aetiologies.
Lumbosacral radiculopathies
o Neuropathy involving the nerve root. It can also be caused by compressive, infectious, malignant, and inflammatory aetiologies.
What are the causes of compressive neuropathies?
Compressive neuropathies produce symptoms in the distribution of the affected nerve root, plexus, or individual nerve. Causes includes solid tumours, abscess, haematoma or metastases.
Cancer can produce nerve dysfunction secondary to compression by solid tumours, infiltration by malignant cells, or paraneoplastic immune-mediated attack.
What is peroneal neuropathy?
Peroneal neuropathy is the most common mononeuropathy affecting the lower extremity, usually manifesting as foot drop. Most often, the nerve is injured at the fibular neck due to compression (e.g., surgical positioning, crossing legs, or trauma).
The peroneal nerve is derived from the L4-S1 nerve roots. These fibres travel through the lumbosacral plexus and eventually the dorsal component of the sciatic nerve. Within the sciatic nerve, fibres of the common peroneal nerve run separately from the tibial fibres. Near the fibular neck, the common peroneal nerve divides into its terminal branches, the superficial and deep peroneal nerves. Isolated deep peroneal neuropathies are less common.
What are the infectious causes of neuropathy?
Viral infections such as herpes zoster virus, herpes simplex virus (HSV), Epstein-Barr virus (EBV), and cytomegalovirus (CMV) can involve nerve roots, leading to a painful radiculitis, or may trigger a Guillain-Barre syndrome 1 to 3 weeks after infection.
This is more commonly seen in people with altered immune function: for example, older people or those with HIV.
What is the presentation of vasculitic neuropathy?
Vasculitic neuropathy usually occurs suddenly and is painful. The typical vasculitic picture is stepwise involvement of multiple individual nerves (mononeuritis multiplex) rather than an isolated mononeuropathy. Because individual nerves are affected, one does not see the distal and symmetrical (e.g., stocking-glove) distribution of deficits typical of a generalised polyneuropathy, at least early on. In advanced cases, however, a confluent pattern can emerge that mimics that of a length-dependent polyneuropathy.
What is the presentation of neuropathies?
It is important to characterise the neurological symptoms being experienced by the patient.
Sensory symptoms
-Patients should be encouraged to describe their symptoms in detail in their own words.
-Common descriptions include burning, stabbing, pins and needles, prickling, stinging, and sharp shooting pains. It is important to establish whether there is an associated loss of sensation, and whether it is in the same area as the paraesthesias.
-Painful paraesthesias suggest an inflammatory or ischaemic process such as vasculitis. Shooting pains are characteristic of nerve entrapment.
Motor symptoms
-Associated symptoms of motor weakness or gait abnormalities (e.g., a foot drop) should also be assessed.
Localisation
- The localisation of the symptoms provides clues as to the affected nerve and site of compression.
- Nerve root compression produces symptoms in the distribution of the affected dermatome and myotome. Plexopathies produce symptoms in the distribution of multiple peripheral nerves from the plexus. Compression or injury of isolated nerves distal to the plexus produces symptoms in the distribution of the individual nerve.
Constitutional symptoms
-Weight loss, night sweats, and/or fatigue may be present in infection, neoplastic disease, or a range of inflammatory conditions. Dry eyes or mouth may indicate Sjogren’s syndrome.
Skin and joint changes
-Ulcers, purpura, rash, or darkening of the skin may suggest peripheral vascular disease, infection, vasculitis, monoclonal protein production, or sarcoidosis. Arthralgias, joint swelling, or stiffness may indicate a rheumatological condition.
What are the investigations for neuropathy?
EMG
Nerve conduction studies
Imaging such as CXR
What is foot drop?
Foot drop is an abnormal walk (gait) that is caused by a tendency of the front half of the foot to drop downwards as you walk along. Your foot can catch on the floor as you swing your leg forwards to take a step.
What is the gait of the foot drop?
As you walk along, the affected foot (or feet) catches on the floor.
As you walk along you lift the leg high to avoid the foot catching (high stepping gait). People who do this often tend to walk on tiptoe on the other side to equalise the sides.
As you walk you swing the affected leg out to the side to avoid it catching on the floor.
What is the aetiology of foot drops?
Foot drop is usually caused by a malfunction of a nerve in the lower leg called the common peroneal nerve.
The most common causes are:
- Injury to the common peroneal nerve.
- Lower back damage (including a ‘slipped’ disc (prolapsed disc) affecting the nerves in the lower leg).
What is the common peroneal nerve?
It’s a small nerve that branches off from the sciatic nerve in the thigh. It runs down the back of the knee and winds around the top of the fibula to go into the muscles of the lower leg. It is very near the surface at this point and can be easily bruised or compressed.
Which activities increases your risk for foot drop?
Activities that compress this nerve can increase your risk of foot drop.
Examples include:
-Crossing the legs. People who habitually cross their legs can compress the peroneal nerve on their uppermost leg, particularly if they are slim.
-Prolonged kneeling. Occupations that involve prolonged squatting or kneeling can result in temporary foot drop. Certain yoga positions can also cause nerve compression resulting in foot drop.
-Wearing a leg cast. Plaster casts that enclose the ankle and end just below the knee can exert pressure on the peroneal nerve and cause foot drop.
What are the other causes of foot drop?
Hip replacement. Knee surgery. Sciatic nerve damage. Cauda equina syndrome. (This is compression of the nerves in the tail of the spinal cord, usually caused by a 'slipped' disc or tumour.) Diabetes with peripheral neuropathy. Stroke. Transient ischaemic attack (TIA). Multiple sclerosis (MS). Cerebral palsy. Charcot-Marie-Tooth disease. Poliomyelitis (rarely causes isolated foot drop). Motor neurone disease. Friedreich's ataxia. Brain tumour. Adverse drug or alcohol reaction.
What are the investigations for foot drop?
X-rays USS CT scan MRI EMG and nerve conduction studies.
