Clinical approach
The CD4 count is a useful guide to the aetiology of a neurological presentation - toxoplasmosis and cryptococcal meningitis occur at CD4 counts below 200∕mm3 whereas CMV complications occur below 50∕mm3.
Since HIV infection itself results in CSF abnormalities such as a raised white cell count and an elevated protein level, more specific tests are required to diagnose encephalitic and meningitic illnesses. These include the measurement of cryptococcal antigen levels in cases of meningitis due to C. neoformans and CSF-VDRL and TPHA if syphilis is a differential. The inflammatory response is impaired and patients with meningitis may present with only mild symptoms of headache and no neck stiffness or photophobia. The threshold for investigating with CT∕MRI and lumbar puncture is necessarily low. The measurement of serum antibodies to diagnose, for example toxoplasmosis, is unhelpful since the usual rise in levels of IgM does not occur. Infection with more than one organism occurs not infrequently, for example Cryptococcus neoformans and Mycobacterium tuberculosis and needs to be considered in cases of non-response or deterioration.Box 8.3 Clinical guidelines
• CD4 useful guide to aetiology
• Persistent CSF abnormalities due to HIV
• Reduced inflammatory response
• Impaired antibody response
• Multiple simultaneous infections
• Maintenance treatment required
Box 8.2 Neurological complications in HIV infection
Opportunistic infections
• Toxoplasma gondii — abcesses and encephalitis
• Cryptococcus neoformans — meningitis
• JC virus — leucoencephalopathy (PML)
• CMV — retinitis, encephalitis, cauda equina syndrome, mononeuritis multiplex
Tumours
• Primary CNS lymphoma
HIV-related disorders
• HIV- associated dementia complex
• Vacuolar myelopathy
• Peripheral neuropathy (distal sensory polyneuropathy)
• Polymyositis
Figure 8.1 Management of mass lesions in HIV infection. * MRI is preferred mode of imaging. # If significant mass effect treat with reducing course of dexamethasone in addition to toxoplasma therapy