Thickened nerves is a physical sign that can occur in few diseases. Leprosy is by far most common cause of thickened nerves.
Therefore most of the clinical examination of thickened nerves is also based on experience with leprosy.
How to Palpate Thickened Nerves
For examination of thickened nerve, the tips of the index, middle and ring fingers, the nerve is rolled backwards and forwards across the long axis of the nerve.
The sites of palpation are suggested in figure.
- Superficial radial nerve running over the extensor pollicis tendon,
- Ulnar nerve behind the medial epicondyle at the elbow
- Common peroneal nerve around the fibula head
- Terminal sprigs of the peroneal nerve over the dorsum of the foot.
It must be noted that mildly thickened nerve is difficult to appreciate. A comparison with opposite side may help.
Causes of Thickened Nerve
Leprosy is a neurpathy and is the only condition in which a palpably hypertrophied peripheral nerve is often central to the diagnosis.
The likelihood of detecting one or more enlarged nerves varies from 20% -96% of the patients.
The nerves in the upper limbs are more often affected than those of the lower. The most commonly involved nerves are the ulnar, median, posterior auricular, superficial radial, common fibular, superficial fibular and posterior tibial.
In 90% of those patients with nerve enlargement, it is detectable in either the ulnar or the peroneal nerve.
After leprosy treatment nerve may gradually shrink, but they remain abnormally firm.
Localized hypertrophic neuropathy
It is a nerve condition in which nerve cells increase in number and form bundles that look like onion bulbs and usually affect one nerve, usually in an arm or leg.
The clinical profile is suggested by muscle weakness, numbness, and decreased reflexes which get worse over time.
Treatment usually consists of having surgery to remove the abnormal part of the nerve.
Acromegaly is a hormonal disorder that develops when your pituitary gland produces too much growth hormone during adulthood.
It is characterized by enlargement of hands, feet, forehead, jaw, and nose and spectrum of other symptoms like joint pain, thicker skin, deep voice and vision problems.
Nerves can get thickened due to enlargement of perineural fibrous tissue. Median nerve is most commonly nerve involved. Ulnar nerve symptoms have also been described.
Neurofibromatosis is one of the neuro-cutaneous disorders characterised by pigmented macules (cafe-au-lait spots), tumours of skin and nervous system.
In neurofibromatosis, generalised nerve thickening is only sporadically reported and can be mistaken for nerve thickening of leprosy.
Both, even may coexist. A nerve biopsy may be required to differentiate.
Diabetic neuropathies result from diabetic microvascular injury involving small blood vessels that supply nerves in addition to macrovascular conditions that can culminate in diabetic neuropathy.
Diabetic neuropathy is associated with changes in the extracellular matrix of the perineurium, including thickening of the basement membrane of the perineurial cells.
Hereditary Motor and Sensory Neuropathy
This group involves Charcot–Marie–Tooth disease and other neurpathies and remains one of the significant causes of thickened nerves after leprosy.The term HSMN is less commonly with the identification of a wide number of genetically and phenotypically distinct forms of Charcot–Marie–Tooth disease.
Palpable nerve thickening occurs in about 30% of patients with demyelinated form but not the axonal form of hereditary motor and sensory neuropathy. The best nerve to palpate is the greater auricular nerve, which cannot usually be felt in normal people.
Cause of nerve thickening in is thought to be the summation of onion bulb formation around individual dysmyelinated nerve fibres.
Refsum disease is one of a family of genetic disorders known as the leukodystrophies in which, as a consequence of the disruption of lipid metabolism leading to accumulation of phytanic acid.
Diffuse nerve enlargement occurs in some patients with Refsum’s disease. Other features are ataxia, retinitis pigmentosa and hearing impairment due to phytanic acid deposition.
In amyloidosis, a nerve might get infiltrated with amyloid protein and cause palpable enlargement. It is very rare though.