Pressure mild or intermittent initially damages myelin sheath& NCS will show slowing of conduction over the relevant site.
Sustained or severe pressure damages the integrity of the axons , with loss of the sensory action potential distal to the compression.
Certain conditions increase susceptibility to develop entrapment neuropathies as: acromegaly, hypothyroidism, pregnancy, any pre-existing mild generalized axonal neuropathy (e.g. DM)& bone damage near the nerve.
Patients with multiple recurrent entrapment neuropathies, esp at unusual sites, should be screened for AD hereditary neuropathy with liability to pressure palsies (HNPP).
Unless axonal loss has occurred, entrapment neuropathies will recover if the pressure relieved, either by avoiding precipitating activities or limb positions, or by surgical decompression.
Entrapment neuropathies Nerve Symptoms Muscle weakness/muscle-wasting Area of sensory loss Median (at wrist) (carpal tunnel syndrome) Pain /d paraesthesia on palmar aspect of hands &fingers, waking the patient from sleep. Pain may extend to arm and shoulder Abductor pollicis brevis Lateral palm & thumb, index, middle and medial half 4th finger Ulnar (at elbow) Paraesthesia on medial border of hand, wasting & weakness of hand muscles All small hand muscles, excluding abductor pollicis brevis Medial palm & little finger& medial half 4th finger Radial Weakness of extension of wrist and fingers, often precipitated by sleeping in abnormal posture, e.g. arm over back of chair Wrist and finger extensors, supinator Dorsum of thumb Peroneal Foot drop, trauma to head of fibula Dorsiflexion and eversion of foot Nil or dorsum of foot Lateral cutaneous nerve of the thigh (meralgia paraesthetica) Tingling / dysaesthesia on lateral border of the thigh Nil Lateral border of thigh
Investigations in NEUROPATHIES: First-line tests Second-line tests Occasionally useful tests Haematology Full blood count ESR B 12 / folate Biochemistry Urea, electrolytes, calcium Serum lipids, lipoproteins Vit as B12,E Creatinine Cryoglobulins Phytanic acid (Refsum's disease) Liver function tests Toxic metal / drug screen FBS,GTT/HbA lc Prostate-specific antigen Thyroid function tests Urinary porphyrins Plasma protein electrophoresis Urinary Bence Jones protein Faecal occult blood Immunology VDRL Antiganglioside antibodies Serum autoantibodies (ANF, dsDNA, RF, extractable nuclear antigens) Antineuronal antibodies Other Nerve conduction/EMG Genetic screening tests (e.g. hereditary neuropathies, Friedreich's ataxia) Chest X-ray/CT Mammogram, Abd imaging
When multiple nerve root, peripheral nerve or cranial nerve lesions occur serially or concurrently , the pathology is due either to involvement of the vasa nervorum (vasculitis or DM) or malignant infiltration of the nerves.
The clinical expression of a very widespread multifocal neuropathy may become confluent so that the clinical picture eventually resembles a polyneuropathy.
In this case neurophysiology may be required to identify the multifocal nature of the problem.
Investigation of patients with an acute multifocal neuropathy should be urgent since vasculitis is a common cause, either as part of a systemic disease or isolated to the nerves.
The clinical effects of a generalised pathological process occur in the longest peripheral nerves first, affecting the distal lower limbs before the upper limbs, with sensory symptoms & signs of an ascending 'glove/stocking' distribution.
This is particularly true with axonal neuropathies where the disorder affects the metabolic processes required for axonal transport in the peripheral nerves as DM.
In inflammatory demyelinating neuropathies, the pathology may be more patchy & variations from this ascending pattern occur.
Develops 1-4 weeks after respiratory infection or diarrhoe a (particularly Campylobacter ) in 70%.
There is a predominantly cell-mediated inflammatory response directed at the myelin protein of spinal roots, peripheral & cranial nerves, triggered by molecular mimicry between epitopes found in the cell walls of some micro-organisms & gangliosides in the Schwann cell membranes.
The resulting release of inflammatory cytokines blocks nerve conduction followed by a complement-mediated destruction of the myelin sheath &the associated axon, if it is severe.
The CSF protein is elevated at some stage of the illness but may be normal in the first 10 days.
There is usually no rise in CSF cell number (a lymphocytosis of > 5 × 107 cells/litre suggests an alternative diagnosis).
Electrophysiological studies are often normal in the early stages but show typical changes after a week or so, with conduction block & multifocal motor slowing, sometimes most evident proximally as delayed F-waves.
Investigation to identify an underlying cause, as CMV, mycoplasma or Campylobacter , requires a chest X-ray, stool culture & appropriate immunological blood tests.
Antibodies to the ganglioside GQ1b are found in the Miller Fisher variant.
Acute porphyria should be excluded by urinary porphyrin& serum lead should be measured if there are only motor signs.
During the phase of deterioration, regular monitoring of respiratory function (vital capacity /arterial blood gases) is required, as respiratory failure may develop with little warning & require ventilatory support.
Ventilation may be needed if the vital capacity < 1 litre, but intubation is more often required because of bulbar incompetence leading to aspiration.
General management & physiotherapy to protect the airway ,prevent pressure sores &venous thrombosis is essential.
Corticosteroid ineffective, but, plasma exchange & IV immunoglobulin shorten the duration of ventilation & improve prognosis, provided treatment is started within 14 days of the onset of symptoms, but no further advantage of combining both.
Causes: hereditary,metabolic as DM or immune-mediated (including abnormal paraproteins).
Many abnormal genotypes cause hereditary demyelinating peripheral neuropathies with variable phenotypes, most characteristically that known as Charcot-Marie-Tooth (CMT) produces distal wasting ('inverted champagne bottle' or 'stork' legs), often with pes cavus&a predominantly motor clinical involvement. In 70-80% PMP-22 gene on chromosome 17 (autosomal dominant CMT type 1).
Evolving over months or years, is the most frequently seen form of neuropathy.
In 30% of patients no cause can be established, even after thorough investigation.
These patients usually have a mild axonal neuropathy , causing unpleasant symptoms, but does not lead to motor disability.
If a patient with what seems to be an idiopathic polyneuropathy progresses to significant disability, finding a specific cause (usually inflammatory or genetic or metabolic as DM) needed.
Myopathies: hereditary Gower sign Calf p hypertrophy Winging scapula Type Inheritance . Age at onset. Muscles affected & associated signs. Duchenne MD. Becker Limb girdle. Fascio scapulo humeral Myotonia dystrophica. X linked Res. = AutosoRes. Autoso dominan Autosom D. 3 to 10 ys. Older 10 to 30 ys. 10 to 40. Any( 20 to 60) Proximal legs & arms ,then generalized. Pelvic or shoulder girdle or both. Less sever,may reach adulthood. Fascial ,shoulder & seratous anterior. Temporalis, fascial, sternocleidomastoid, distal limbs ptosis, catarct, testicular atrophy, frontal baldness & myotonia(slow relaxation of contracting muscles).
Diagnosis : Muscle enzymes as CPK –MM (myocardial band) which is very high in Duchenne & normal or moderately increased in others. EMG &muscle biopsy. Management: No specific treatment except for physiotherapy & rehabilitation ,although there reports of benefit of steroids in DMD. Genetic counseling: DMD & Myotonia Dyst. Can now be diagnosed by DNA analysis even in the preclinical period or in female carriers or during pregnancy Appropriate advice can be offered to couples before marriage or before deciding to have a child or to decide on abortion .
Prognosis : DMD & Myotonia Dystr. Die with HF & respiratory failure DMD within 10 years of diagnosis life span of FSH & limb girdle is not affected.
Toxic myopathies : Caused by: toxins as alcohol drugs as carbinoxolone, thiaxide, diuretics, steroids & penicilamine. Metabolic & endocrine myopathies: Causes of acute muscle weakness : Electrolyte abnormalities as hypo & hyperkalemia , hypo & hypercalcemia familial periodic paralysis which may be hypokalemic, normokalemic or hyperkalemic. Causes of chronic metabolic or endocrine proximal myopathies affecting proximal shoulder & pelvic girdle include: hyperthyroidism , hypothyroidism, cushing , Addison & it may be the first presentation of endocrine disorders .
MCQs: 1.The following test should be done in ever case of neuropathy to find the cause: A. Complete blood picture. B. ESR. C. ANF. D. Hb1C. E. Serum lead.
MCQs: 2.Bell’s palsy can be causes by: A. Pregnancy. B. HSV. C. VZV. D. Hypertension. E. Sarcoidosis.
MCQs: 3.Bilateral lower motor neuron facial pals is caused by: A. Sarcoidosis. B. HSV. C. VZV. D. GBS. E. Mumps.
MCQs: 4.Gullein-Barre syndrome can follow the following infections: A. CMV. B. Campylobacter. C. Helicobacter pylori. D. Yesrsina. E. E Coli.
MCQs: 5.Gullein-Barre syndrome can be manifested by the following: A. Autonomic dysfunction. B. Ataxia. C. Bulbar paralysis. D. subjective sensor loss. E. Opthalmoplegia.
MCQs: 6.Gullein-Barre syndrome bad prognostic features include: A. Young age. B. Early nerve conduction study changes. C. Respirator paralysis. D. Axonal loss on NCsS. E. Bulbar paralysis.
MCQs: 7. Bad prrognostic signs in Bells palsy include: A. Young age. B. Partial paralysis. C. Nerve conduction abnormalities early in the course. D. Nerve conduction abnormalities after the first week. E. Idiopathic type.
MCQs: 8. AIDP differs from CIDP by: A. Response to IVG. B. Response to plasmophariesis. C. Response to steroides. D. The causes. E. Prognosis.