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: