WHAT IS TABES DORSALIS
Tabes Dorsalis is a parenchymatous form of neurosyphilis characterized clinically by ataxia of the lower limbs, lightning pain, loss of jerks, Argyll-Robertson’s pupil and pathologically by the degeneration of the posterior column of the spinal cord.
PATHOLOGY OF TABES DORSALIS
Macroscopically there is atrophy of dorsal spinal nerve roots in lower thoracic and lumbosacral region. The posterior column of spinal cord is wasted, hence the name Tabes dorsalis.
Microscopically there is degeneration of exogenous fibers, that is central processes of posterior root ganglia but the ganglia themselves are little affected. The most accepted theory is meningeal construction of these fibres at the point where they enter the pia mater.
CLINICAL FEATURES OF TABES DORSALIS
ONSET IS GRADUAL
Age: Usually 30-45 years but even in younger age group it may occur (Juvenile Tabes)
Symptoms appear between 8-12 years after exposure to infection, rarely as early as 3 years. There are few diseases which may give rise to so many varied symptoms and signs.
So it was previously told that “know syphilis and the rest of Medicine will be known to you.
These are due to involvement of the posterior column or nerve root.
(a) Lightning pain: This is the earliest symptom. But in course of time patient may forget about it. This comes suddenly, persists for few seconds or minutes, passes transversely, usually affects the lower limbs, comes at irregular intervals, stabbing in character, changes in intensity with change of weather and barometric pressure, may precede other symptoms by 5-10 years. Occasionally vasodilatation and ecchymoses of the skin may be seen on the site of pain. This is due to involvement of the posterior nerve root.
(b) Paresthesia of lower limbs, numbness, coldness, sensation of walking on cotton and wool may be present.
(c) Impairment of deep pain sensation occurs early. Joint sensation is also lost. Impairment of cutaneous pain and touch sensation develops in some selected areas, e.g. across the chest, lower part of shin bones, on the nose and central part of face (Tabetic mask), on the ulnar borders of forearm and perianal area. Deep painful stimuli are appreciated after a long interval. From these areas anaesthesia starts and may ultimately involve the whole body. Deep pain sensation is lost in tendoachilis and sometimes in testicles.
(d) Vibration sense is lost and this may be the first sign of the disease. This is due to involvement of posterior column fibres.
Due to involvement of posterior nerve root, reflex pathway is interrupted and reflexes are gradually lost. Loss of ankle jerks is first seen and the earliest change is asymmetry followed by loss of knee jerks (Westphal’s sign).
Abdominal reflexes are exaggerated due to irritation of the posterior nerve roots and planter reflex remains unchanged. There is also difficulty in initiating the act of micturition which is called stammering of bladder. There may be retention of urine and faeces and rarely unconscious evacuation. Recurrent infection of bladder may lead to ascending pyelonephritis which is a common cause of death in tabes dorsalis. Impotency may develop early when sacral roots are involved.
(a) Hypotonicity of muscles: Muscle tone is gradually diminished so much so that abnormal range of active and passive movements are possible. Genu recurvatum may develop.
(b) Ataxia: Due to lesion of the postrior nerve roots, fibres carrying the sense of position are affected. This is seen in the lower limbs first. The difficulty is first manifested during co-ordinated movements without the help of vision. This is called spinal ataxia and is manifested with closed eyes. This is the basis of a postitive Romberg’s test where patient is unable to stand with apposed feet and closed eyes. Finger nose test also becomes positive in cervical tabes.
CRANIAL NERVE FUNCTION
(a) Ocular disturbances: Most important and characteristic pupillary change is Argyll-Robertson pupil. This is possibly due to involvement of both colliculonuclear fibres and sympathetic fibres in the periaquiductal zone.
This is characterised by the following:
(ii) Bilateral involvement.
(iii) Ecentric pupil.
(iv) Irregularity of the pupil due to atrophy of the iris.
(v) Pigmentation of iris.
(vi) Light reflex is lost.
(vii) Accommodation reflex is present and brisk.
(viii) Mydriatics act very very slowly.
In course of time primary optic atrophy develops. The Peripheral visual field is constricted while central vision remains intact but in some cases central scotoma may develop. In many patients when optic atrophy is well-pronounced, minimal symptoms and signs of ataxia are present in lower limbs. This inverse relationship is sometimes observed and this is called Benedict’s law.
Due to involvement of sympathetic fibres there is pseudoptosis (as a result of paralysis of tarsal muscle), ocular fissure is diminished and to overcome pseudoptosis there is compensatory wrinkling of forehead. These constitute so-called Tabetic facies.
(b) Other cranial nerve involvement: Lesions of various cranial nerves may give rise to loss of smell (olfactory nerve), loss of taste (trigeminal nerve), pain and analgesia on the face (trigeminal nerve), deafness and vertigo (auditory nerve).
Several crises are seen. These are characterised by paroxysms of painful disorders of functions referable to some organs. Crises may begin suddenly, last for hours to days and disappear abruptly. Of various types, gastric crisis is commonest and important. This consists of nausea, vomiting, epigastric pain or discomfort.
Similarly, there are rectal (tenesmus), laryngeal (stridor, dyspnoea, cough), vesical (strangury), cardiac (precordial pain) crises.
These crises are probably due to severe spasm of hollow viscera due to disorder of autonomic nervous system.
There may be trophic ulcers either on the heel or on the ball of the great toe. These are painless with indurated margins and the depth is upto bone. Charcot’s joint is another form of trophic change. The knee and hip loints are commonly affected. The affected joint becomes disorganised, there is enormous effusion inside the joint, the ends of bones forming the joint and periarticular tissues are all wasted. The range of movement is increased and there may be easy dislocation. The characteristic feature is complete absence of pain.
Patient stands on broad base and usually supports himself on a stick. During walk the foot is raised to a high level as there is loss of sense of position (high stepping gait) and during stepping heel touches the floor first suddenly as there is loss is sense of position. This is called Tabetic or stampring gait or gait of spinal ataxia. Unsteadiness of gait is more marked at night.
These patients are usually lean and thin and do not put on weight even if they live on high caloric diet.
There is loss of motor power, wasting of muscles, no papillary changes. Sensory loss limited over stoking and gloves area and not on the nose or chest. Calf muscles are tender.
Subacute combined degeneration of the Spinal cord
Planter reflex is extensor in type, blood picture shows pernicious anemia, bone marrow shows megaloblastic reaction and gastric secretion shows histamine fast achlorhydria.
Ataxia is of cerebellar type, plantar reflex is extensor in type, light reflex is present, intention tremor and scanning speech develop.
There may be nystagmus and optic atrophy. Planter reflex is extensor, pes cavus, scoliosis and cardiomyopathy are present.
Myotonic pupil of Adie and Fostermoore
It is common in young females with loss of tendon reflexes. Pupillary change is usually unilateral. The affected pupil larger with regular outline and reacts very slowly to light. The reaction to light is slower than the reaction to accommodation. The condition is usually asymmetric. But sometimes patient may complain of inability to focus with the affected eye. 2% Methacholine instillation into the conjunctival sac will produce constriction of Adie’s pupil but not of Argyll-Robertson’s pupil.
VDRL and FTA-ABS tests may be positive in more than 70 % of cases. CSF shows increased lymphocytes with normal or increased protein. Lange’s colloidal gold curve shows Tabetic curve. The serologic tests are positive.
1. Specific treatment-see below.
2. For lightning pain, analgestics, e.g., Aspirin may be tried. Steroids and heavy dose of neurotropic vitamins may be used. Exposure to cold is avoided. Recently Carbamazepine (1600 mg daily) or Phenytoin (300 mg daily) are found to be useful.
3. Ataxia may be minimised by re-education with the help of Frenkel’s exercise.
4. Bladder symptoms: For precipitancy of micturition atropine substitutes may be used. If there is cystitis it should be treated with urinary antiseptic drugs. Catheterisation should be done to find out the amount of residual urine.
5. Charcot’s joints: Immobilisation of the joint is to be done and movements are to be restricted as far as practicable.
6. For crises, sedatives like Pethidine 100 mg IM or surgical procedures may be adopted. Adrenalin, 0.5 ce (1: 1000) subcutaneously may be helpful.
For optic atrophy-Long continued steroid therapy is beneficial.