Vacuolar myelopathy is a neurological disorder that primarily affects the spinal cord. It is strongly associated with advanced human immunodeficiency virus (HIV) infection. This condition leads to progressive neurological symptoms, impacting a person’s mobility and sensation over time.
What is Vacuolar Myelopathy?
Vacuolar myelopathy is characterized by the formation of numerous small cavities, or vacuoles, within the white matter of the spinal cord. These spaces develop from the breakdown of myelin, the protective sheath around nerve fibers, and fiber swelling. The most commonly affected areas are the lateral and posterior columns of the spinal cord, particularly in the thoracic region, though it can also involve the cervical or lumbar spinal cord.
This condition is considered the most common spinal cord disease in individuals with HIV/AIDS. While often observed in the later stages of AIDS when CD4+ lymphocyte counts are very low, it can, on rare occasions, be an initial sign of HIV infection. Vacuolar myelopathy shares pathological similarities with subacute combined degeneration of the spinal cord, a condition typically linked to vitamin B12 deficiency.
Symptoms and Progression
Symptoms typically involve a slow, progressive worsening of neurological function over several months. Individuals often experience progressive weakness, predominantly in their lower extremities. This weakness can lead to significant gait disturbances, such as unsteadiness, difficulty walking, and an uncoordinated, stiff gait known as spastic paraparesis.
Sensory abnormalities are common, including numbness, tingling, and impaired vibration sense or proprioception in the legs. As the condition progresses, individuals may develop bladder and bowel dysfunction, manifesting as urinary urgency, incontinence, or even erectile dysfunction in men. The disease generally follows a progressive course, potentially leading to severe paralysis and loss of sphincter control over time.
Understanding the Causes
The cause of vacuolar myelopathy remains unclear, but theories suggest factors related to HIV infection. One prominent hypothesis points to metabolic derangements, specifically involving the vitamin B12-dependent transmethylation pathway. This pathway is responsible for producing S-adenosyl-methionine (SAM), a molecule important for nerve health. Impaired utilization of vitamin B12 can lead to abnormal SAM production, which may explain the pathological resemblance to vitamin B12 deficiency myelopathy.
Another theory involves neurotoxic factors. These are substances secreted by HIV-infected cells or immune cells that respond to the infection. These factors are thought to directly damage the spinal cord tissue, contributing to the formation of vacuoles.
Diagnosis and Management
Diagnosis is often a process of exclusion, ruling out other spinal cord dysfunctions. This diagnostic workup typically includes magnetic resonance imaging (MRI) of the spinal cord. While MRI may show spinal cord atrophy or areas of increased signal on T2-weighted images, particularly in the thoracic spine, findings can also appear normal.
Laboratory tests are also performed, including serologic tests to confirm HIV infection and to rule out other conditions like vitamin B12 deficiency. In some cases, cerebrospinal fluid (CSF) analysis may be conducted, which might show a normal or mildly elevated protein level or a slight increase in lymphocytes. Differential diagnoses that need to be considered include other infections, tumors, or nutritional deficiencies affecting the spinal cord.
There is no cure for vacuolar myelopathy, and treatment options are limited. While antiretroviral therapy (ART) is the cornerstone of HIV management and can improve overall health, its effect on vacuolar myelopathy varies among patients. Supplementation with vitamin B12 or L-methionine has not shown proven benefit. Management largely focuses on symptomatic treatment, such as medications to alleviate spasticity and manage bladder dysfunction, along with physical and occupational therapy to help maintain function and mobility.