Diseases Of The Central Nervous System

DISEASES OF THE CENTRAL NERVOUS SYSTEM

CEREBRAL EDEMA may be vasogenic or, less commonly, cytotoxicThis

edemaVasogenic : Results from increased pressure or permeability of capillaries and venules : It is usually seen around Brain abscesses .1 Brain tumors .2 Brain contusions .3 Brain infarcts .4 The accumulated fluid is intercellular

:Cytotoxic edema Results from cell injury with metabolic derangements The accumulated fluid is intracellular :Effects of cerebral edema Increased intracranial pressure which may be followed by brain herniation

HYDROCEPHALUS :Definitions Hydrocephalus: Increased volume of CSF within the cranial cavity Internal hydrocephalus (or simply “hydrocephalus”): Increased CSF within the ventricular system which thus becomes enlarged External hydrocephalus: Increased CSF within the sub-arachnoid space Communicating hydrocephalus: Hydrocephalus in which CSF flows freely from ventricular system into sub-arachnoid space Non-communicating hydrocephalus: Hydrocephalus in which CSF does not flow freely from ventricular system into sub-arachnoid space Compensatory hydrocephalus: Increased volume of CSF consequent to loss of brain tissue

: Causes .1Increased production of CSF seen in association with papillary tumors of the choroid plexus .2Decreased absorption of CSF occurring in association with subarachnoid hemorrhage (due to obliteration of the arachnoid villi by ( hemosiderin-containing macrophages .3Cerebral atrophy . The hydrocephalus here is not accompanied by increased intracranial pressure .4Obstruction to CSF flow . This is the commonest cause of hydrocephalus. : It may result from a) Congenital stenosis of ventricular foramina or aqueduct b) Pressure on the ventricular foramina or aqueduct by an intracranial tumor, brain abscess or tuberculoma c) Meningitis due to obliteration of 4th ventricle foramina or sub-arachnoid space following organization of the inflammatory exudate in the base of the brain

:Pathology Obstruction of one of the foramina of Monroe leads to .1 enlargement of one lateral ventricle Obstruction of the third ventricle or aqueduct leads to .2 enlargement of both lateral ventricles Obstruction of the foramina of the 4th ventricle leads to .3 enlargement of the entire ventricular system .4Obstruction at the sub-arachnoid space also leads to enlargement of the entire ventricular system but, in contrast to the above three conditions,the hydrocephalus is of the communicating type

:Effects Enlargement of the head if the .1 hydrocephalus develops before closure of the cranial sutures ((children Enlargement of the .2 ventricles and atrophy of brain tissue Increased intracranial pressure .3

INCREASED INTRACRANIAL PRESSURE An increase of CSF pressure above 200mm. water with the patient recumbent Causes: Increase of the intracranial volume, mainly :due to Brain edema .1 Hydrocephalus .2 Intracranial hemorrhage .3 Brain abscess .4 Intracranial tumors .5

:Clinical manifestations Headache .1 Vomiting .2 Papilledema (edema of the optic disc) caused by .3 compression of the retinal vein as it traverses the subarachnoid space in the optic nerve sheath Increased systolic BP .4 Slow pulse .5 Decreased consciousness & eventually coma .6

HERNIATION OF THE BRAIN Expansion of the brain particularly when localized may lead to displacement of the brain against the falx cerebri or the tentorium cerebelli. If the ,expansion is severe enough herneation of the brain will occur i.e. protrusion of a part of the brain most commonly under the falx or through the tentorial appreture or the foramen .magnum

:Possible effects arteries

Compression of anterior or posterior cerebral .1

Compression of third cranial nerve .2 Compression of the brain stem with distortion of the .3 respiratory centers in the medulla Obstruction of CSF flow through the fourth ventricle .4 leading to further increase of intra-cranial pressure Hemorrhage into the pons & midbrain .5

CEREBRO-VASCULAR DISEASES Abnormalities of the brain resulting from .pathological processes of blood vessels The term “stroke” is the clinical designation applied to these diseases particularly when symptoms .develop acutely The major cerebro-vascular diseases are thrombosis ,embolism andhemorrhage. The first two often lead tocerebral infarction

:CEREBRAL INFARCTION :Risk factors Atheroma - Hypertension - Abnormal serum lipids Coronary artery disease - Cardiac failure Smoking - Atrial fibrillation - Diet - Obesity Alcohol

:Causes Thrombosis.1: on top of atherosclerosis of a) Anterior, posterior & middle cerebral arteries b) Basilar artery c) Internal carotid arteries d) Vertebral arteries The commonestintra-cranial site of thrombotic vascular occlusion is themiddle cerebral artery The commonestextra-cranial site of thrombotic vascular occlusion is the origin of aninternal carotid artery

Embolism:from thrombi in .2 a) The left side of the heart: vegetations of subacute bacterial endocarditis or mural thrombi in atrial fibrillation or myocardial infarction b) The aorta c) Neck arteries

:Miscellaneous causes .3 a) Systemic circulatory insufficiency in the presence of severe atherosclerotic narrowing of cerebral or neck arteries b) Arteritis , either infective or due to collagen diseases c) Blood diseases e.g polycythemia, sickle cell disease d) Pregnancy and perpeurium e) Oral contraceptive pills f) Drug addiction

:Pathology Thecommonest site for infarction is the distribution of the middle cerebral artery i.e.basal ganglia and internal capsule Grossly, the infarct may be hemorrhagic or pale & eventually undergoes liquefaction & absorption to be replaced or surrounded .by glial tissue

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:Effects Depend on the site of the infarct, most commonlyhemiplegia due to destruction of the pyramidal tract in the internal capsule

SPONTANEOUS INTRACEREBAL :(INTRAPARENCHYMAL) HEMORRHAGE :Risk factors Hypertension - Vascular malformations - Arteritis Bleeding diathesis

:Causes Hypertension due to rupture of one of the .1 numerous micro-aneurysms found in the brain, usually following a sudden rise of blood pressure. .This is the commonest cause Rupture of Vascular malformations .2 Hemorrhage into a brain tumor .3 Blood diseases e.g acute leukemia .4

:Pathology Thecommonest site is the region of the basal ganglia & internal capsule The blood in the brain may dissect its way until it reaches the ventricles or the sub-arachnoid space

:Effects Sudden severe rise of intracranial pressure .1 Herniation of the brain .2 Signs of meningeal irritation if the blood reaches .3 the subarachnoid space Hemiplegia due to destruction of the pyramidal .4 tract in the internal capsule

:SUB-ARACHNOID HEMORRHAGE s:Cause (Rupture of a berry aneurysm (65% .1 (Rupture of a vascular malformation (5% .2 Extension of intracerebral or intraventricular .3 hemorrhage into the sub-arachnoid space Blood dyscrasias .4 (Unknown cause (25% .5

:Berry (sacular, congenital) aneurysm Occurs in arteries of the circle of Willis at the base of the brain in1 - 2% of adults and is multiple in 10 - 15%. of cases It results from a congenital defect in the .media of the artery at a bifurcation

:Other types of aneurysms Atherosclerotic aneurysm: fusiform, .1 mostly in the basilar artery Mycotic aneurysm: resulting from .2 destruction of the vessel wall by mild inflammation e.g following impaction of emboli derived from vegetations of subacute bacterial endocarditis

:Effects of aneurysms Rupture leading to sub-arachnoid .1 hemorrhage : Berry aneurysm usually ruptures between 40 and 50 years of age and atherosclerotic aneurysm in the 6th decade or later Thrombosis in the aneurysm which .2 may lead to brain infarction Hydrocephalus .3

:Vascular Malformations Include:cavernous angiomas ,capillary telangiectasias (hemangiomas) andarteriovenous malformation. (AVM) which is the most important AVM appearsgrossly as a mass of tortuous blood vessels occuring most commonly in relation to .the middle cerebral artery It may rupture leading tosub-arachnoid or intracerebral hemorrhage most commonly between the ages of 10 and 30 yrs

INFECTIONS OF THE CNS :PYOGENIC INFECTIONS Acute suppurative ( pyogenic, bacterial, septic) :meningitis Acute suppurative inflammation of the leptomeninges ((pia/arachnoid :Causative organisms Niesseria meningitidis (meningococcus): the commonest .1 E.coli: in neonates .2 Other organisms: Strept. pneumonie, H. influenzae .3

:Mode of Infection Droplet inhalation from nasopharyngeal carriers. .1 The organisms reach the meninges via the blood stream. This isthe usual mode of infection particularly in meningococcal meningitis Local spread of infection from middle ear or .2 paranasal sinuses Direct infection through a compound fracture of .3 the skull

:Pathology :Gross The sub-arachnoid space is .1 filled with pus, thickest and most abundant in the base of the brain and the sulci The meningeal vessels are .2 dilated and engorged with blood

:Microscopic The sub-arachnoid .1 space is filled with neutrophils, pus cells and fibrin The meningeal vessels .2 dilated & engorged with blood

:CSF Changes Increased amount, under pressure and turbid or .1 frankly purulent Increased protein .2 Increased cells, mainly neutrophils .3 Markedly decreased or absent glucose .4 Causative organism are present & can be .5 detected in Gram- stained films or after culture

:Effects & Complications :Septicemia which may lead to .1 a)Acute bacterial endocarditis b)Acute adrenal insufficiency due to hemorrhage in the adrenals ( glands (Waterhouse-Friderichsen syndrome Hydrocephalus .2 Ptosis, diplopia and squint due to damage of the 3rd, 4th and 6th .3 cranial nerves following organization of the inflammatory exudate in the base of the brain Vascular thrombosis which may lead to ischemic lesions of the .4 brain Encephalitis due to direct spread of infection to the brain .5 Increased intracranial pressure .6

:Brain Abscess Causative organisms: The commonest are Staph and Strept :Mode of infection Local spread of infection from suppurative otitis media, .1 mastoiditis or sinusitis Blood-borne infection from suppurative diseases of the lung .3 (vertebral system of veins) or, less commonly, acute (bacterial endocarditis (systemic pyemia Direct infection through a compound fracture of the skull .2

:Sites .1Temporal lobe in cases complicatingotitis media .2Cerebellum in cases complicatingmastoiditis .3Frontal lobe in cases complicatingsinusitis .4Parietal lobe and cerebellum in cases complicatingsuppurative lung diseases .5Multiple abscesses allover the brain inpyemia

:Pathology :Acute abscess An irregular cavity with a thin wall, filled with fluid pus and surrounded by a zone of congestion :Chronic abscess A regular, spherical or oval cavity with a thick fibroglial wall and a smooth lining, filled with thick .pus Microscopically, fibrous tissue, hypertrophied astrocytes and foamy macrophages are seen in the abscess wall

:Effects & complications Increased intracranial pressure .1 Focal neurological manifestations depending on .2 the site of abscess Hydrocephalus .3 Rupture into the sub-arachnoid space or .4 ventricles leading to meningitis

:TUBERCULOSIS Is alwayssecondary and usually results fromhematogenous dissemination of .a tuberculous focus elsewhere in the body It takes two main forms : tuberculous meningitis and tuberculoma

:Tuberculous meningitis

:Mode of infection Blood-borne infection .1 Rarely, local spread of infection from a .2 tuberculous vertebral body

:Pathology :Gross A gelatinous exudate is found at the base of the .1 brain Minute tubercles may be detected in the .2 (meninges or the surface of the brain (hand lens :Microscopic A tuberculous reaction with obliterative endarteritis is seen in the meninges

:CSF Changes Increased volume, under pressure and clear or .1 opalescent Increased protein .2 Increased cells, mainly lymphocytes .3 Normal or slightly reduced glucose .4 A fine fibrin web develops on the surface of on .5 standing

:Effects & Complications Ptosis, diplopia & squint .1 Hydrocephalus .2 Focal neurological manifestation due to small .3 brain infarcts resulting from obliterative endarteritis Increased intracranial pressure .4

:Tuberculoma A localized tuberculous lesion that appears grossly as a well circumscribed, often encapsulated mass that may show central caseous necrosis or dystrophic .calcification It is oftenmistaken clinically and radiologically for an.intra-cranial tumor

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:Effects Increased intracranial pressure .1 Focal neurological manifestations .2 Hydrocephalus .3 Rupture into subarachnoid space causing .4 tuberculous meningitis

:NEUROSYPHILIS Although spirochetes may reach the CNS as early as the second stage of syphilis, lesions appear only in the third stage (tertiary or meningo-vascular syphilis) or as late as 20 years after the primary infection (quaternary or parenchymatous syphilis which includes general paralysis of the insane and .(tabes dorsalis

:Tertiary neurosyphilis :Characterised by A subacute meningitis with gummas .1 Syphilitic obliterative endarteritis .2 which may lead to focal ischemic lesions in the brain

:(General Paralysis of the Insane (GPI Characterised by a subacute encephalitis :which leads to Progressive dementia .1 Various motor and sensory disturbances .2

:Tabes Dorsalis Characterized bydegeneration of posterior spinal nerve roots (most commonly the lumbo-sacral) leading loss of sensation with consequent degenerative changes in the joints Charcot’s joint ) andataxia)

VIRAL INFECTIONS :OF THE CNS Virusesreach the CNS by theblood stream or rarelyalong peripheral nerves.( (rabies virus They mayenter the body: through The skin or mucous membranes (Herpes simplex .1 ( virus The alimentary tract (enteroviruses), or by .2 (Arthropod (insect) bites (arboviruses .3 Viral infections of CNS may take the form of : viral (aseptic) meningitis or viral encephalitis

:Viral aseptic meningitis A mild, usually self-limited meningitis Caused most commonly by one of the enteroviruses Pathology: Infiltration of meninges and subarachnoid space by lymphocytes, plasma cells and macrophages :CSF changes Pressure slightly increased .1 Protein slightly to moderately increased .2 Cells increased, mainly lymphocytes .3 Normal glucose level .4

:Viral encephalitis A viral infection of the brain parenchyma, almost always accompanied by inflammation of meninges (meningo-encephalitis) and sometimes with simultaneous involvement of the spinal cord ((encephalo-myelitis

Common microscopic :features Perivascular & .1 parenchymal infiltration by lymphocytes & plasma cell Neuronal degeneration .2 neuronophagia &

(Glial cell reaction (gliosis .3

:Poliomyelitis An acute viral infection of the anterior horn cells of the spinal cord, particularly those of the lumbar and cervical enlargements, leading to paralysis of limb muscles. Motor nuclei of the .brain stem are also commonly affected It usually occurs in infants & young children and may appear in sporadic or epidemic forms

Cause: Poliovirus, an RNA enterovirus Mode of infection: Ingestion of food or drink contaminated by the virus, which multiplies in the mucosa and lymphoid tissue of the intestine, then travels to the (CNS via the blood stream (viremia Incubation period: 1 - 3 weeks

:Pathology Perivascular infiltration by lymphocytes and .1 plasma cells Degeneration of the neurons and neuronophagia .2 Wallerian degeneration and demyelination in the .3 axons of motor neurones Denervation atrophy of muscles supplied by .4 damaged neurons

:Clinical features Prodromal stage characterized by fever, .1 headache, maliase, nausea, vomiting and sore throat. It either subsides (abortive :poliomyelitis) or progresses to Preparalytic stage characterized by stiffness of .2 the neck, pain in the back and limbs and signs of meningeal irritation. It either subsides or :progresses to Paralytic stage characterized by flaccid paralysis .3 of limb muscles

:Rabies Cause:

Rhabdovirus, an RNA virus

Mode of infection: Bite of a rabied animal, most .commonly a dog The virus is present in the saliva of the animal that .contaminates the bite wound .It travels to the CNS along peripheral nerves IP: 1-3 months depending on the distance between the bite and the CNS

:Pathology A severe diffuse viral encephalitis is seen, .affecting mainly the gray matter It is distinguished from other viral infections of the brain by the presence of characteristic eosinophilic inclusions in the cytoplasm of the damaged neurons known asNegri bodies. Rabies virus can be detected within these bodies by electron microscopy or immunohistochemistry

:Clinical Features The earliest symptom is hydrophobia (spasm of .1 (the pharyngeal muscles on attempt to drink Excitability .2 Flaccid paralysis .3 Death results from respiratory center failure .4

DEMYELINATING DISEASES

Acquired conditions characterized by destruction of myelin with relative .preservation of axons The most important are multiple (disseminated) sclerosis and acute disseminated encephalomyelitis

:MULTIPLE SCLEROSIS

.The commonest demyelinating disease Characterized by multiple foci of demyelination & gliosis in the brain & spinal cord :Pathology Grossly, discrete foci of demyelination & gliosis known asplaques are seen, most commonly around the ventricles and in the brain stem, spinal cord & optic nerves

,Microscopically :Acute lesions show Demyelination with infiltration.1 by lipid containing macrophages (gitter cells) Perivascular infiltration by lymphocytes and plasma .2 cells Old lesions show replacement of the cellular infiltrate by gliosis

:Clinical Features The disease is rare in childhood and after the age .1 of 50 years It is chronic characterized by relapses and .2 remissions over many years Clinical manifestations include abnormalities of .3 vision, parasthesia, paraplegia and ataxia depending on the area of the CNS affected

:Etiology Not established but the following factors may ed:involvbe Genetic factors .1 Environmental factors .2 Immunological factors : MS may result from an .3 autoimmune reaction against a neural tissue component OR an abnormal immune response to a neurotropic virus

:ACUTE DISSEMINATED ENCEPHALOMYELITIS Ausually self-limited demyelinating disease occuring in children and young adults, following :either An acute viral disease eg mumps, measles, .1 rubella, chicken pox (post-infectious (encephalomyelitis A viral immunization ( .2post-vaccinal (encephalomyelitis Itmay be due to an autoimmune reaction against myeline basic protein or an abnormal immune response to virus or virus-infected cells

DEGENERATIVE DISEASES Diseases of the gray matter characterized by progressive loss of neurons in the absence of any previous or associated neurological .disease The most important are Alzheimer’s disease and motor neurone disease

:ALZHEIMER’S DSEASE A degenerative disease of the CNS .characterized by progressive dementia It usually begins after the age of 50 years and is the commonest cause of dementia .in the elderly It is commoner in females

:Etiology :Obscure but the following factors may be involved A genetic predisposition as supported by the following .1 : observations a) The disease is familial in 5 - 10% of cases b) Pathological changes identical to those of Alzheimer’s disease are seen in patients with trisomy 21 (Down’s syndrome) who survive beyond the age of 45 yrs Slow viral infection .2 Trauma .3 Intoxication by heavy metals eg lead .4

:Pathology .1Grossly , the brain is atrophied, weighing 1000g. or less. The atrophy is most marked in the frontal lobes .2Microscopically:, there is a) Generalized loss of neurones and gliosis b) A large number ofsenile (Alzheimer’s) plaques in the gray matter, composed of masses of argyrophilic filaments and granules, often having a central core ofamyloid material c) A large number ofneurofibrillary tangles in the cytoplasm of neurones , appearing as bundles of argyrophilic filaments that surround or displace the nucleus

:MOTOR NEURONE DISEASE A degenerative disease of the CNS characterized by .progressive loss of motor neurons in adults It is commoner in males and is . usually fatal in 2-3 yrs Theetiology unknown but genetic factors , infection by polio virus and intoxication by heavy metals may be involved

Threevariants: are recognized Progressive muscle atrophy with selective .1 involvement of the cervical spinal cord Progressive bulbar palsy with involvement of .2 cranial nerve nuclei in the brain stem Amyotrophic lateral sclerosis with involvement of .3 upper motor neurones

TUMORS OF THE CNS :GENERAL CONSIDERATIONS Distinction between “benign” and “malignant” lesions is less sharp .1 than in other organs The anatomic location of the neoplasm can have lethal .2 consequences irrespective of its histologic type Even the most aggressive types rarely metastasize ouside the .3 CNS, however, they may become disseminated by the CSF to other sites in the CNS.CSF dissemination occurs most commonly with ependymoma and medulloblastoma .4Common effects include: Increased intra-cranial pressure, brain herniation, hydrocephalus, brain edema, hemorrhage, and focal neurologic manifestations depending on the site of the tumor Most arise from glial cells, particularly astrocytes i.e. are .5 astrocytomas

:GLIOMAS :Derived from glial cells and include Astrocytomas derived from astrocytes .1 Oligodendroglioma derived from oligodendroglia .2 Ependymomas derived from epedymal cells .3

:ASTROCYTOMAS I. Diffuse fibrillary astrocytoma (WHO grade II :(astrocytoma Sites: Most common in cerebrum Age: (Most common in adults (30 – 50 years Gross appearance: Poorly defined, firm or soft grayish mass

:Microscopic Consists of stellate astrocytes irregularly distributed in a fibrillary background made up of astrocytic cell processes :Prognosis Moderate with a mean survival of 5 years

II. Anaplastic astrocytoma (malignant :(astrocytoma, WHO grade III astrocytoma Differs from diffuse fibrillary astrocytoma as :follows More cellular .1 Shows nuclear pleomorphism and mitosis .2 Shows mild endothelial cell proliferation .3

III. Glioblastoma multiforme (GBM, WHO grade IV :(astrocytoma :Differs from grade III astrocytoma as follows Grossly, .1well demarcated and often shows necrosis and hemorrhage on the cut surface More cellular .2 Shows more nuclear pleomorphism and more frequent mitosis .3 Shows multinucleate tumor giant cells .4 Shows marked endothelial cell proliferation leading to “glomeuloid .5 “bodies Shows areas of necrosis surrounded by “pseudopalisades” of .6 neoplastic cells

Prognosis of anaplastic :astrocytoma and GBM Very poor particularly for GBM which has a mean survival of 8 – 10 months

IV. Pilocytic astrocytoma (WHO grade I :(astrocytoma Sites: Most common in the cerebellum, the floor and walls of the third ventricle and the optic nerves Age: Children and young adults Gross: Cystic with a “mural nodule” in the cyst wall

Microscopic:: Consists of Cellular areas made up of bipolar cells .1 with long, thin processes Less cellular areas with microcysts and .2 Rosenthal fibers Prognosis: Very good

:NEURONAL TUMORS The most important iscerebral neuroblastoma which occurs in children and ismalignant with a poor prognosis. It resembles peripheral .neuroblastomas microscopically

:POORLY DIFFERENTIATED (EMBRYONAL) TUMORS The commonest is Medulloblastoma :Medulloblastoma Age: Mostly children Site: Exclusively, thecerebellum Gross: Awell defined, soft, gray mass mostly located in the (midline of the cerebellum (vermis

:Microscopic A highly cellular tumor composed of sheets of small, undifferentiated cells with scanty cytoplasm and hyperchromatic nuclei, forming variable numbers ofHomer-Wright rosettes

:Prognosis The tumor ishighly malignant and commonly disseminates by CSF. However, it ismarkedly radiosensitive, so that the 5-year survival after total excision may be as high as 75%

:OTHER PARENCHYMAL TUMORS Primary brain lymphoma .1 Germ cell tumors .2 Pineal body tumors .3

:MENINGEOMAS Benign tumors that arise from the meningothelial cells of the arachnoid Age: Adults Site: Along the surfaces of the brain, rarely within the ventricular system Gross: Well encapsulated, firm grayish mass, attached to the dura and compressing the brain

Microscopic:: There are several histologic patterns Syncytial (meningothelial), composed of .1whorls of oval cells with indistinct cell boundaries. A variable number of calcospherules (psammoma bodies) are present in the centers of the neoplastic cell whorls Fibroblastic, composed of fascicles of spindly cells resembling .2 fibroblasts Transitional, showing features of syncytial and fibroblastic types .3 Psammomatous containing numerous psammoma bodies .4 Angioblastic which is .5highly vascular and folows anaggressive behavior. This now considered to bea hemangiopericytoma of the brain rather than a type of meningioma

:PERIPHERAL NERVE SHEATH TUMORS :(Schwannoma (neurilemoma .1 A benign tumor derived fromSchwann cells :Sites a) Eighth cranial nerve at thecerebellopontine angle ((acoustic neuroma b) Spinal nerve roots in thespinal canal :Pathology a) Asolitary encapsulated mass, attached to the nerve of origin

b) Microscopically, it shows a biphasic pattern consisting of cellular areas made up of spindly cells showingnuclear palisading (Antoni type A) and less cellular areas made up of stellate cells widely separated by a myxoid stroma containing (microcysts (Antoni type B

: Neurofibroma .2 A benign tumor consisting offibroblasts, Schwann .cells and collagen .Site: Spinal nerve roots in thespinal canal Pathology: Anon-encapsulated mass .“interrupting” the nerve of origin It may besolitary or multiple (in multiple neurofibromatosis or von Recklinghausen’s disease which is an autosomal dominant .(hereditary disorder

:METASTATIC TUMORS Represent 50% of intracranial tumors May occur in the brain or meninges The commonest primary sites are the lungs, breast, kidney and GIT

:PARANEOPLASTIC SYNDROMES Occur most commonly in association with small cell carcinoma of the lung and :include .1Cerebellar degeneration leading to cerebellar signs and symptoms .2Limbic encephalitis leading to subacute dementia .3Subacute sensory neuropathy

DISEASES OF PERIPHERAL NERVES

PERIPHERAL NEUROPATHY A degenerative disease of peripheral nerves leading to muscle atrophy and weakness, sensory disturbances .and autonomic defects

:CAUSES .1Immune-mediated (Acute “idiopathic” inflammatory .( polyneuropathy,Guillain-Barre syndrome .2Infections: Diphtheria, leprosy, varicella zoster .3Diabetes mellitus .4Vitamin defficiencies: Thiamine, B12, B6, E .5Toxic chemicals: Alcohol, lead, arsenic, hydrocarbons .6Drugs: Diethyl hydantoin, dapsone ( .7Malignancies (paraneoplastic syndromes

:GUILLAIN-BARRE SYNDROME . This is thecommonest peripheral neuropathy It is usuallypreceded by an acute influenza-like .illness . It is most probablyimmunologically mediated Most cases recover in one to several weeks but rare cases develop chronic disease with .relapses and remissions

TUMORS OF PERIPHERAL NERVES .1SCHWANNOMA (NEURILEMOMA): See tumors of CNS .2NEUROFIBROMA: This may change into a malignant peripheral nerve sheath tumor particularly in patients with neurofibromatosis ((see tumors of CNS .3MALIGNANT PERIPHERAL NERVE SHEATH TUMOR (MALGNANT SCHWANNOMA, NEUROFIBROSARCOMA): Rare. May arise de novo or in a neurofibroma, particularly in patients with neurofibromatosis