Normal pressure hydrocephalus in adults

Early detection of hydrocephalus in adults greatly improves outcomes, says Dr Tillmann Jacobi.

Hydrocephalus is not always a feature of childhood. About one in 100,000 adults, usually over the age of 60, develops normal pressure hydrocephalus (NPH). This accounts for up to 40 per cent of all cases of hydrocephalus.

Research suggests that between 2 and 5 per cent of patients over the age of 60 who are thought to have dementia have NPH which could be treatable.

NPH can initially present as low mood or apathy, which could be misinterpreted as clinical depression or, for example, a prolonged bereavement reaction.

In NPH sufferers, the amount of cerebrospinal fluid (CSF) produced is normal, but that its flow and re-absorption is blocked.

The usual amount of CSF in the adult brain is between 120ml and 150ml, but it can increase to over 200ml. Gradually this will lead to an enlargement of the ventricles and compression of the brain tissue. Eventually this compression will result in partial or total loss of the brain functions of these compressed areas.

NPH is a mechanical problem and, although the precise physiological reasons for its development still remain particularly unclear, known risk factors are closed head injuries, intracranial infections or haemorrhages, tumours and previous surgery.

Symptoms and diagnosis

Patients often experience a certain set of symptoms with gradual onset, which are different to those shown by children with hydrocephalus.

The symptoms can seem unspecific at first, or could be related to some of the typical problems found in older patients.

However, in combination, the symptoms could prompt the clinician to consider NPH.

The typical triad of symptoms and signs are gait disorders, urinary incontinence and increasing memory loss, which can progress to dementia.

Gait problems can be a subtle and general imbalance and unsteadiness, but will progress to a walk with wide-based, short, slow, shuffling movements, falls without loss of consciousness, unexplained weak-ness in the legs and possibly complete immobility.

Initial features of urinary urge incontinence tend to worsen gradually, sometimes despite medical treatment.

The memory problems are, as in dementia, often the last symptom to become obvious and are undeniable to the patient and their relations.

Due to the absence of abnormalities of the cranial nerves, other obvious neurological deficits or pain, it can be very difficult to reach the diagnosis clinically. Sometimes Romberg testing and plantar reflexes are abnormal.

Lumbar puncture usually shows normal pressure because the enlarged ventricles will have accommodated the extra volume of CSF.

However, a suspicion of NPH should prompt a CT or MRI scan of the head, and referral for the intracranial pressure to be measured.

If left untreated the prognosis for NPH is poor and the condition will prove to be life limiting. Early diagnosis offers an increased chance of minimising progression or even reversal of symptoms.

Surgical drainage

Once the diagnosis is confirmed, a temporary lumbar drainage of the CSF may lead to an almost instant partial reversal of the problems of gait, incontinence and memory loss.

However, in many cases, the symptoms worsen again after a while and continuous drainage via a surgical shunt is likely to be necessary.

These shunts usually drain CSF from the brain into the atrium of the heart or into the peritoneum. Unfortunately we cannot predict or guarantee to what degree the shunt will help the individual patient. In cases detected early, there is a 90 per cent chance of improving, while in others it may be 50 per cent or less.

The patient is unlikely to experience drastic improvements straight after the surgery. This is because the amount of drainage of CSF is controlled by a valve to prevent overdrainage.

The valve will be set initially at a low level and over the weeks and months after surgery it can be gradually opened until the desired improvements are seen without adverse effects. This means regular follow-ups, which will be necessary for life.

Lifestyle change

NPH and its treatment is a traumatic and stressful experience for the patient. The condition and treatment involves lifestyle changes because the valve and tubing system are placed superficially under the skin and can thus be damaged fairly easily by trauma.

Flow changes may occur when the shunt is exposed to too much heat.

Antibiotic prophylaxis before dental procedures and other surgical interventions is recommended.

Educating the patients and their carers about the condition is essential to enable early identification of problems or malfunction of the shunt.

- Dr Jacobi is a salaried GP in York

KEY POINTS

- NPH accounts for up to 40 per cent of all cases of hydrocephalus.

- NPH might present as low mood or apathy.

- The amount of CSF is normal but its flow and re-absorption are blocked.

- Gait disorders, urinary incontinence and increasing memory loss are typical features.

- Continuous surgical drainage is necessary.

REFERENCES

- Czosnyka M, Pickard J D: Monitoring and interpretation of intracranial pressure. J Neurol Neurosurg Psychiatry 2004 Jun; 75(6): 813-21

- Poca M A, Mataro M, Del Mar Matarin M: Is the placement of shunts in patients with idiopathic normal-pressure hydrocephalus worth the risk?

Results of a study based on continuous monitoring of intracranial pressure. J Neurosurg 2004 May; 100(5): 855-66.

RESOURCES

Association of Spina Bifida and Hydrocephalus - www.asbah.org.

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