Infections of the nervous system II

Spinal infections

Specific infections of the spinal cord are caused by viruses such as HTLV-1, polio, herpes zoster, herpes simplex and Epstein–Barr, bacterial and other infections including syphilis (see below) and Lyme disease. Infection can also spread from the spine. The spinal cord and cauda equina may also be affected by meningitic processes described previously and in association with meningoencephalitis.

HTLV-1 is a retrovirus. It is common in the West Indies, Africa and southern USA and in immigrants from these areas. Myelopathy occurs in a small proportion of seropositive patients (2–5%) and presents as a slowly progressive weakness and stiffness in the legs with sensory symptoms and prominent bladder symptoms. The arms are rarely affected. Oligoclonal bands are positive in the CSF. The main differential diagnosis is with multiple sclerosis. Treatment is symptomatic.

Poliomyelitis is now extremely rare. It can lead to a myelitis and leave significant neurological deficit (p. 109).

Other viruses, particularly from the herpes group, can produce a transverse myelitis, though this is usually in the immunocompromised.

Pyogenic infection in the vertebral body or in the epidural space can lead to an epidural abscess (Fig. 1), producing back pain often associated with fever. This is followed by radicular pain and then symptoms and signs of spinal cord or cauda equina involvement. If this diagnosis is suspected then urgent investigation with spinal MRI is needed, as early drainage of the abscess and high-dose antibiotics is the only hope of reversing this process. A similar, if slower, onset is associated with tuberculous epidural abscess. Treatment of this is primarily antituberculous therapy, though in some patients surgery is needed.

Fig. 1 MRI showing epidural abscess associated with discitis leading to spinal cord compression. The abscess is the ring enhancing lesion (arrowed).

Peripheral nerve infections

The most common peripheral nerve infection is shingles (5 per 1000 per year), resulting from herpes zoster dorsal root ganglionitis. This is usually thoracic and can be managed conservatively. When it occurs in unusual sites or more than one dermatome, it is useful to consider whether there is an underlying cause for immunosuppression. When it occurs in the ophthalmic branch of the trigeminal nerve, there is particular concern as this innervates the cornea and corneal ulcers can occur. Neuralgic pain may develop following the infection, which usually settles spontaneously but sometimes persists. Oral aciclovir shortens the illness and reduces the frequency of post-herpetic neuralgia. Aciclovir eye drops are used in ophthalmic zoster. Carbamazepine and amitriptyline are helpful in patients with post-herpetic neuralgia.

Syphilis

Syphilis used to be the great mimic in neurology and syphilis serology was performed on all patients with neurological disease. Neurosyphilis is now rare. Pathologically, neurosyphilis occurs because of a chronic syphilitic meningitis and an endarteritis. These result in a large number of neurological abnormalities that can be categorized into four neurological syndromes, most of which occur years after the original infection:

The diagnosis of syphilis is in two phases. Blood serology (TPHA, VDRL and FTA) identifies patients with current or prior infection. CSF examination is used to determine the activity of infection, measuring cell count, protein and VDRL titre. Treatment is with prolonged (21 days) supervised courses of intramuscular penicillin.

Tropical neurology

Infections play a larger part in neurology in tropical countries. For example, cysticercosis, schistosomiasis and paragonimiasis (oriental liver fluke) are common causes of seizures in different parts of the world. Cerebral malaria is a common cause of coma and death in parts of Africa. All these conditions are seen in people who have travelled in tropical countries, so a travel history is an important clue in the diagnosis of these conditions.

The immunocompromised host

Immunocompromised patients most commonly have:

iatrogenic cause for immune suppression, such as chemotherapy

severe general illness such as diabetes or lymphoma

a specific immune deficiency such as AIDS.

The first two of these are associated with an increased risk of infection from bacteria and fungal infections. This can involve organisms that are not usually pathogenic. Infection can be difficult to diagnose as there may not be the normal immune response and related clinical features. So in an immunocompromised patient with meningitis there may be a fever and malaise but without symptoms and signs of meningeal inflammation, headache and neck stiffness.

There are some types of infections that occur especially in certain patient groups, for example listeria meningitis in alcoholics and fungal infection in profoundly neutropenic patients. A wide range of neurological problems occurs in human immunodeficiency virus (HIV) infection and AIDS.

HIV infections and AIDS

Neurological complications can occur at any stage of HIV infection. At seroconversion, Guillain–Barré syndrome and facial weakness have been documented. During the asymptomatic phase of HIV infection, chronic demyelinating neuropathies may occur.

Most neurological problems in HIV infection occur as the patient develops significant immunosuppression. Opportunistic infections, tumours, specific neurological problems associated with HIV and neurological complications of the treatment of HIV infection then occur. Different levels of the nervous system are affected and are summarized in Table 1.

Toxoplasmosis

This presents with a focal neurological deficit, headache or seizures, usually developing over a few weeks (Fig. 2). Brain scanning reveals single or multiple ring-enhancing masses with oedema. As this is the most likely diagnosis in this setting, a trial of anti-toxoplasma treatment is given. Further investigation is considered if this fails. The most common differential diagnosis is primary CNS lymphoma. This can be treated with radiotherapy but the response and prognosis are poor.

Fig. 2 Toxoplasma abscesses in AIDS: pre (a) and post (b) treatment.

Peripheral neuropathies

These are common in AIDS. Some distal symmetrical neuropathies are due to agents such as didanosine and zalcitabine. In others, the aetiology is unknown. Mononeuritis multiplex associated with vasculitis can occur.

Infections of the nervous system II

Epidural abscess is a rare cause of radicular pain and fever. This is a medical emergency.

Syphilis is rare but can produce a wide range of neurological problems.

The immunocompromised host can develop a wide range of unusual infections.

HIV is associated with infections at every level of the CNS.