Spinal cord may be involved by a number of conditions ranging from trauma, neoplasmas, inflammatory process, immunological reactions to vascular causes.
All these causes are known to produce features of compression of the cord leading to motor weakness of the limbs. But there are a number of conditions which produce picture of myelopathy but without any evidence of any mechanical obstruction.
These conditions come under the heading of ‘Non-compressive myelopathy’ which has been defined as “acute subacute or chronic involvement of the cord with a without involvement of the nerve roots and peripheral nerves due to multiple causes and in whom there is no myelographic evidence of obstruction or arachnoiditis.”
A broad classification of diseases causing non- compressive myelopathy is as follows.
1. Viral: Enteroviruses, herpes zoster, poliomyelitis, rabies.
2. Bacterial: Tuberculosis, syphilis, pyogenic infections.
3. Immunoalleigic: Influenza and other viral infections.
Post exanthematous (measles, chickenpox, rubella)
Post vaccinal (rabies, tetanus, smallpox, poliomyelitis).
4. Demyelinating disorders: Multiple
sclerosis, neuromyelitis optica (Devic’s disease)
5. Heredofamilial/degenerative disorders
a. Motor neurone disease
b. Hereditary spastic paraplegia
c. Hereditary ataxias
6. Toxic myelopathy
– Subacute Myelooptic neuropathy (SMON)
7. Arteriosclerotic Myelopathy
8. Myelopathy due to physical agents:
Irradiation, electrical injury.
9. Nutritional myelopathy: Subacute combined degeneration of the cord.
10. Non-metastatic carcinomiatous myelopathy.
It occurs in middle age or elderly who develop either a slowly progressive spastic paraplegia or lower motor neurone lesion involving the lower limbs with variable sensory loss. There are signs of generalized atherosclerosis, disease of vertebral artery or vascular complications of diabetes.
Hypertension or collagen disorder. Often there is occlusion of anterior spinal artery which is a major supplier to the substance of the cord. Depending on the level of occlusion, clinical signs are present.
Besides pyramidal and spino thalamic tracts there is impairment of sphincter control. Arterial pulses in the lower limbs are diminished. X-ray of abdomen may show calcification in aorta and its branches.
Vascular malformations a period ranging upto several years and result into parapresis with involvement of various tracts. One third of the patients may have an abrupt attack which simulates Acute myelitis while others have radicular pains in the back.
Pathogenesis of this form of myelopathy is not well understood but probably it is necrotic non-inflammatory process which produces ischemia of the cord.
Spinal cord infarction results due to ischemia which is secondary to distant vascular occlusion. It generally occurs in a vascular area round about thoracic cord. It appear suddenly like stroke, Rarely it may be associated with systemic arteritis, immune reaction or to microscopic fragments of herniated nucleus pulposus after minor trauma.
Recovery is generally slow but may start within a few days on the onset of symptoms. Treatment is of underlying pathology.
These include cases of Multiple sclerosis. Devic’s disease (neuromyelitis optic) and schilders disease. Onset is generally insidious with a progressive motor and sensory deficit.
In Devic’s disease the transverse necrotic lesion of cord occurs before or shortly after optic neuritis. The post infectious demyelinating disorders are usually non-recurring and cause symptoms related to a single level of the cord.
Here not only cord but also meningeal involvement may take place.
Rabies virus (Rhabdovirus) reaches central nervous system along the peripheral nerves and multiplies in the neurons. The patient passes into a stage of encephalitis leading on to paralysis in the limbs. Post rabic vaccinal encephalomyelitis produces motor and sensory disturbances in the limbs with flaccid paraplegia and sphincter disturbances.
Herpes viruses (HSV-1 and 2) Epstein-Ban virus (EBV) are associated with not only lesions of the dorsal roots but also encephalo myelitis leading to involvement of spinal cord. Motor weakness of lower limbs is less common in herpes simplex infection while herpes zoster virus causes cranial and peripheral nerve palsies with encephalomyetitis.
Epstein-Barr virus (EBV) also causes encephalomyelitis but rarely. In the same group influenza and para-influenza also uncommonly involve spinal cord and nerve roots. Patient may have root pains with progressive weakness of the lower limbs and sensory loss with retention of urine.
Poliomyelitis is caused by the polio virus, an RNA virus belonging to enterovirus family. The incubation period varies from 7-14 days and the disease is characterized by fever, back pain and tenderness in muscles which ultimately become weak.
Asymmetrical weakness of lower limbs may develop. Other enterovimses like coxsackie. ECHO and enterovirus 70 may cause a picture like polio though the condition is milder than polio.
The Human retroviruses HTLV-1 and HIV may be associated with myelopathies. HTLV-1 causes a chronic progressive non-inflammatory cord syndrome with symmetric spastic parapresis.
Mild sensory and bladder disturbances may occur, in a sub acute form of encephalitis caused by measles virus which mainly affects young children (subacute sclerosing Panencephalitis (SSPE) there are signs of pyramidal and extra pyramidal lesion with dementia.
Primary HIV involvement of CNS may produce inflammatory demyelinating polyneuropathy where patient has difficulty in walking, motor weakness of legs and sphincter disturbances. About 20% patients of AIDS develop a vacuolar myelopathy where there is progressive parapresis of lower limbs.
There is spastic lesion with involvement of bladder. Besides the above there are rare forms of slow viral infections caused by unconventional virus like agents. These include KURU, a rare form of sub acute spongiform encephalopathy which is common amongst natives of Papua New Guinea who practiced cannibalism.
Patient develops cerebellar ataxia and involuntary movements of limbs. Creutzfeldt-Jakob disease (CJD) is another disease in this group where there is
involvement of pyramidal arid extra pyramidal tracts along with visual disturbances. The disease carries high degree of mortality and no treatment is available.
Spinal cord is involved due to bacteria or mycobacteria which may arise in the context of systemic infections.
Syphilis may produce chronic meningitic lesions resulting in a picture of myelitis and radiculitis.
Tuberculous spinal meningitis is an extension of either intracranial tuberculosis or secondary to tuberculosis of spine (Potts disease). There is swelling of the cord with edema and inflammatory exudate. Clinical features include a acute or sub acute form of myelopathy leading to motor weakness of limbs. Sometimes an ascending form of myelopathy may occur.
Lathyrisim results due to consumption in large amonts of Kesari Dal (Lathyrus Shtivus). Onset of the disease is by agonizing pains in the calf muscles at night and muscle spasms. Three forms of disease are known – Acute, subacute and insidious onset. The main presentation of the disease is spastic form of paraplegia.
Subacute myelo optic neuropathy (SMON) is a toxic non-inflammatory myelopathy with optic atrophy. It is a rare disease and results due to prolonged use of iodochlorhydroxy quinolones (Enterovioform).
There is generally a sub acute form of onset with sensory neuropathy in the lower limbs. Over a period of time patient develops muscular weakness and some degree of visual impairment. This may be followed by optic atrophy.
Myelopathy due to physical agents
Irradiation of the spinal cord occurs when radiation is being given for carcinoma and this produces radiation myelopathy. Electrical injury following severe electric shock may produce damage to the cord at the level of the cervical region resulting into wasting of upper limbs and spastic parapresis. The velocity of current passed shall determine the degree of damage.
Carcinomatous non-compressive myelopathy due to carcinoma some where in the body can produce subacute or chronic forms of myelopathy. Patient generally develops parapresis with sensory loss and loss of sphincter control. These lesions of the cord generally precedes the malignancy. In chronic forms a picture of motor neuron disease is produced.