Syringomyelia is a chronic disorder characterized pathologically by the formation of a cavity situated in relation to the central canal in the spinal cord and extending to the medulla (syringobulbia).
The condition may be congenital or acquired. Both sexes are affected equally but males are more affected than females. Congenital syringomyelia is the result of abnormal closure of central canal of spinal cord during embryonic life, Incomplete closure leaves cavities around which proliferation and cavitation of embryonic cells (spongioblasts) takes place.
These later from glial tissue which undergoes cavitation. This congenital form of syringomyelia may be associated with other developmental defects. A familial and heriditary incidence of Syringomyelia may be seen.
Acquired syringomyelia follows trauma, cystic degeneration of low grade glioma, intramedullary tumour or as a sequlae of meningitis.
The characteristic pathological changes are seen frequently in lower cervical and upper thoracic region which may extend up to medulla and uncommonly into pons.
The cord is enlarged usually in the transverse plane. The cavity containing protein rich yellowish fluid is surrounded by a zone of translucent gelatinous material. The blood vessels show degenerative changes.
The pathological process starts dorsal to the central canal and extends forwards and laterally to involve the anterior horns of grey matter causing atrophy and degeneration of their axons.
Ascending and descending tracts are involved as a result of pressure or as a result of distension of the cavity. Of these fibres carrying pain and temperature and the cortico spinal tracts are involved while spinothalamic tracts, pyramidal tract and posterior columns are involved later on.
The disease generally starts in the age group of 25-40 years. It is an insidious process. In general the symptoms and signs are those of upper and lower motor involvement with peculiar type of sensory loss (dissociated anaesthesia).
The common cervico dorsal involvement presents with weakness and wasting of the small muscles of the hands. There is loss of pain and thermal sensations in the cervicothoracic segments with preservation of touch.
The progressive extension of the spinal lesion causes compression of dorsal spino thalamic tracts on one or both sides leading to loss of appreciation of pain, heat and cold over the lower parts of body. The distribution of dissociated sensory loss may vary depending on the level of interruption of lateral spino thalamic tracts and crossing fibres.
When the lesion reaches upper cervical segments it involves the spinal tract and the nucleus of trigeminal nerve leading to dissociated anaesthesia over the face. Homer’s syndrome may occur due to involvement of sympathetic fibres in the spinal cord or medulla. Loss of sensations exposes the patient to burns and injuries.
Muscular weakness and wasting especially of the small muscles of hands is usually the first motor symptom. It may be bilateral from the beginning or one side may suffer more as compared to other.
As the lesion spreads muscular wasting spreads to forearms, arms shoulder and upper intercostals. Muscular atrophy is limited and becomes complete in the muscles involved. Fibrillation is usually not present.
Extension of the lesion to medulla may involve nucleus ambigous causing paresis of soft palate, pharynx and vocal cords. Other motor functions of cranial nerves are less effected. Nystagmus is a common feature of syringomyelia. Contractures due to muscular atrophy are commonly seen in hands resulting in “CLAW HAND”.
Compression of pyramidal tracts leads to upper motor neurone lesion (spasticity, extensor plantar response) in later stages. Tendon reflexes are diminished in upper limbs while they are exaggerated in lower limbs.
Involvement of bladder and rectum is usually absent or slight. Trophic symptoms are common in cases of syringo myelia. There is hypertrophy of all tissues, thickening of the bones or condition of osteoporosis. Trophic changes develop as a result of sensory loss.
A great number of patients exhibit osteoarthropathy (Charcot’s joints) which frequently involve the shoulders and elbows. The affected joints undergo degenerative changes, get enlarged with presence of loud crepitus. It is painless involvement. There is hypermobiity and laxity of the joint.
The fingers show trophic changes in the form of thickening of the subcutaneous tissue which becomes swollen. Tips become blunted and the knuckle folds thick and coarse. There are vasomotor disturbances rendering them red or even blue. These fingers are termed as ‘Sausage-like’. Incidence of injury is high in these leading to infection and ulceration.
The typical clinical picture of combination of lower motor neurone and upper motor neurone lesions with dissociated anaesthesia makes diagnosis easy. It may have to be differentiated from intramedullary tumour, progressive muscular atrophy and peroneal muscular atrophy.
Plain X-ray of the spine may show evidence of increased interpedicular distance (AP view) and sagittal diameter in lateral views.
Myelography will show widened spinal cord. CT scan reveals the intramedullary cavity. MRI is definitive way to diagnose the condition since it shall outline the cavity. Other associated anomalies may also be outlined.
It is very unsatisfactory.
Surgical measures include syringostomy and drainage of the cavity into sub arachnoid space. Other measures include decompression and incision of posterior aspect of the cord in cases with severe pain and there is evidence of blockage in the sub arachnoid space.
X-ray irradiation of the affected region of the spinal cord is a tried measure. It gives relief to symptoms especially of pain. This measure temporarily arrests the progress of the disease.
Prognosis. Syringomyelia is a progressive disease though in some cases remissions may occur. Sudden death may occur when hemorrhage occurs into the cavity especially when it involves the bulbar region.