AIDS and AIDS-treatment neuropathies

HIV-associated neuropathic pain: epidemiology, pathophysiology and management

Peripheral neuropathy is associated with numerous systemic illnesses including HIV infection. Neuropathic pain constitutes approximately 25-50% of all pain clinic visits. Distal symmetrical polyneuropathy (DSP) is the most common form of peripheral neuropathy in individuals with HIV infection. DSP is distinguished from other forms of neuropathy on the basis of history and neurological examination. The pain associated with DSP can be debilitating. Therefore, it is important to diagnose HIV-associated DSP properly and treat the neuropathic pain in order to improve quality of life. We review the clinical manifestations, epidemiology, pathophysiology and management strategies for HIV-associated DSP.

Novel mechanism of enhanced nociception in a model of AIDS therapy-induced painful peripheral neuropathy in the rat

To elucidate the underlying mechanisms involved in AIDS therapy-induced peripheral neuropathy, we have developed a model of nucleoside analog reverse transcriptase inhibitor-induced painful peripheral neuropathy in the rat, using 2',3'-dideoxycytidine (ddC), 2',3'-dideoxyinosine (ddI) and 2',3'-didehydro-3'-deoxythymidine (d4T), AIDS chemotherapeutic drugs that are also components of AIDS highly active anti-retroviral therapy. Administration of ddC, ddI and d4T produced dose-dependent mechanical hypersensitivity and allodynia. Peripheral administration of inhibitors of protein kinase A, protein kinase C, protein kinase G, p42/p44-mitogen-activated protein kinase (ERK1/2) and nitric oxide synthase, which have demonstrated anti-hyperalgesic effects in other models of metabolic and toxic painful peripheral neuropathies, had no effect on ddC-, ddI- and d4T-induced hypersensitivity. Since suramin, an anti-parasitic and anti-cancer drug, which shares with the anti-retroviral nucleoside analogs, mitochondrial toxicity, altered regulation of intracellular calcium, and a sensory neuropathy in humans, also produced mechanical hypersensitivity that was not sensitive to the above second messenger inhibitors we evaluated the role of intracellular calcium. Intradermal or spinal injection of intracellular calcium modulators (TMB-8 and Quin-2), which had no effect on nociception in control rats, significantly attenuated and together eliminated ddC and suramin-induced mechanical hypersensitivity. In electrophysiology experiments in ddC-treated rats, C-fibers demonstrated alterations in pattern of firing as indicated by changes in the distribution of interspike intervals to sustained suprathreshold stimuli without change in mechanical activation thresholds or in number of action potentials in response to threshold and suprathreshold stimulation. This study provides evidence for a novel, calcium-dependent, mechanism for neuropathic pain in a model of AIDS therapy-induced painful peripheral neuropathy.

Neuromuscular complications in HIV

HIV affects many organs of the body, including the nervous system. As a result, a series of neurologic complications have created challenges for scientists and clinicians alike. Among these, HIV-associated neuropathy and myopathy may occur at all stages of the disease process. Of the neuropathies, distal symmetrical polyneuropathy is the most common form. The pathogenesis of primary HIV neuropathy is unknown. Other types of neuropathy seen in HIV-infected subjects include toxic neuropathy, inflammatory demyelinating polyneuropathy, progressive polyradiculopathy, and mononeuritis multiplex. In this review, we present the clinical manifestations, pathogenesis, diagnosis, and management of different types of neuropathy in HIV infection. Myopathy, another complication of HIV, is not associated with any particular stage of immunosuppression. Symptoms include symmetrical weakness of the proximal muscles in the extremities. Serum creatine kinase levels are often moderately elevated. Electromyography and muscle biopsy are helpful tests for diagnosis. Treatment of HIV myopathy includes corticosteroids, nonsteroidal anti-inflammatory agents, and intravenous immunoglobulin.

Medication-induced peripheral neuropathy

Although not very common, medication-induced neuropathy is a treatable condition and, therefore, is important to identify. Medications continue to grow in number and expand in usage; consequently, toxic neuropathy continues to be relevant to neurologists. Many agents have toxicities that are tolerated because the treatments are necessary, such as therapies for HIV and malignancy. Additional agents to prevent or ameliorate the toxic neuropathy are being sought and trials are ongoing. Certain patients, however, may be at high risk for peripheral nerve toxicity due to genetic factors or another underlying neuropathy. Newer drug-delivery methods, such as viral transfection, may produce less toxicity in the future. The underlying pathomechanisms remain incompletely elucidated; however, apoptosis is emerging as an important final pathway in some forms of toxic neuropathy. Although most cases demonstrate acute or subacute onset after exposure, recent experiences with statin drugs raise the possibility of occult toxic causes of chronic idiopathic neuropathy.