Compression of median nerve as it passes through the carpal tunnel in the flexor retinaculum

thyrotoxicosis, advanced stage of neurological disease such as myopathies and MND. 2. Muscular hypertrophy - occurs in myotonia congenita, in early stages of Duchenne and Becker dystrophy, occasionally in limb girdle dystrophy, in spinal muscular atrophies involving the gastrocnemius and soleus group of muscles, and at times in metabolic myopathies of adult onset. 3. Muscle tenderness - None in dystrophy, motor neurone disease, and syringomyelia. In arthritic atrophy and cervical rib pressure, affected muscles are -tender to pressure while the wasting process is active. In carpal tunnel syndrome production of typical symptoms by digital compression of median nerve in region of transverse carpal ligament or by forcible flexion of the wrist for one or two minutes. 4. Fasciculations - Absent in dystrophy, widespread in motor neurone disease, continuous and marked, inconstant and slight in peroneal muscular atrophy. In cervical rib and arthritic atrophy, fasciculation is present while wasting is in progress, but is not prominent. 5. Myotonia - in myotonic dystrophy. In longstanding cases however, grip myotonia may not be evident because of progressive wasting. 6. Evidence of other signs of diseases in the nervous system - (i) Monoplegia or hemiplegia in disuse or post-paralytic atrophy (ii) Bulbar paralysis in motor neurone disease. (iii) Pain in neck and shoulder in radiculitis. (iv) C. S. F. changes in spinal block. (v) Positive ! VDRL reaction in syphilitic amyotrophy. (vi) Blue line on gums, and anaemia in lead poisoning. 7. Thickening of peripheral nerves - in leprosy and hypertrophic polyneuritis. 8. Sensory changes - (i) Dissociated anaesthesia in syringomyelia, and spinal tumour. (ii) Glove and stocking type anaesthesia in peripheral neuritis. (iii) Paraesthesia of regional distribution in cervical rib pressure and radiculitis. (iv) Sensory loss in peroneal muscular atrophy. 9. Reflexes - Exaggeration of deep jerks and extensor plantar response in syringomyelia, spinal tumour, amyotrophic lateral sclerosis and pachymeningitis III. Investigations -1 Haematological and biochemical -to demonstrate nature of primary disorder to which muscular wasting is secondary in case of systemic, inflammatory or metabolic disease 2 Serum creatine kinase (CK) -Very high levels in Duchenne and Becker dystrophies, acute polymyositis, and acute myoglobinuric myopathies In other myopathies it may be normal or only moderately raised. 3. EMG - distinguishes myopathic weakness from that due to chronic denervation or to defective neuromuscular transmission as in myasthenic syndrome. 4. Nerve conduction velocity - Normal in myopathies and spinal muscular atrophies, reduced in demyelinating polyneuropathy. 5. Muscle biopsy and histochemical analysis - Infiltration with fat and connective tissue to varying extent in muscular dystrophies, often with abortive regenerative activity. In polymyositis necrotic changes with inflammatory cell infiltration in perifascicular distribution. Normal in most metabolic myopathies. Electron microscopy useful in some metabolic and rare congenital myopathies. 25. PERIPHERAL NEUROPATHY Pathophysiology - Three basic pathological processes affect peripheral nerve fibres - 1. Wallerian degeneration - follows transection of an axon by crushing or injury, with the myelin sheath and axon degenerating distal to the site of division. 2. Axonal degeneration - Most common change, metabolism of the neurone usually affected, resulting in degeneration of the distal portion of the axon. 3. Segmental demyelination - results from disease of the Schwann cell or from a direct attack on the myelin, and the myelin sheath is primarily destroyed leaving the axon intact. Clinical classification - 1 Mononeuropathy or focal neuropathy -Single nerve involved CAUSES - (a) COMPRESSION - e g compression of radial nerve against humerus (Saturday night palsy) (b) ENTRAPMENT -eg. (i) Carpal tunnel syndrome - Compression of median nerve as it passes through the carpal tunnel in the flexor retinaculum at the wrist Causes - (i) Wrist fracture. (ii) Arthritis of the wrist particularly RA. (iii) Soft tissue thickening in myxoedema and acromegaly. (iv) Oedema, notably associated with pregnancy Obesity. (v) No obvious cause More common in women Symptoms - Pain, numbness and paraesthesiae in the hand Pain may radiate to through forearm and occasionally involve the whole arm Typically pain is most troublesome at night or first thing in morning Signs - Weakness of abductor policis brevis, with or without wasting, and also weakness of opponens _ Sensory impairment - of median distribution. Positive Tinel sign - Gentle tapping over carpal tunnel causes paraesthesiae in part of the cutaneous distribution of the nerve. Treatment - (i) Mild case - Wrist splint, diuretics and injection of hydrocortisone into carpal tunnel may give temporary relief. (ii) In severe case - Surgical decompression of carpal tunnel. (c) OTHER CAUSES -Trauma, fractures operations, penetrating injuries, lacerations and injections. 2. Multiple mononeuropathy (mononeuritis multiplex or multifocal neuropathy) - More than one and at times many, individual nerves affected in a patchy distribution CAUSES - (a) Vascular - Diabetes, rheumatoid arthritis, polyarteritis nodosa, SLE, Wegners granulomatosis. (b) Inflammatory - Leprosy, sarcoidosis. (c) Infiltrations - Malignancy, amyloid. (d) Immune reactions - Vaccinations, foreign sera and proteins (e) Physical injury - Trauma, electrical injury.