The virus is spread through sexual contact, use of illegal injected drugs, exposure to blood, or breastfeeding.
People have weakness, stiffness, and muscle spasms in the legs, making walking difficult, and many have urinary incontinence.
To diagnose the disorder, doctors ask about possible exposure to the virus and do magnetic resonance imaging, a spinal tap, and blood tests.
Drugs, such as corticosteroids, may help, and spasms are treated with muscle relaxants.
(See also Overview of Spinal Cord Disorders Overview of Spinal Cord Disorders Spinal cord disorders can cause permanent severe problems, such as paralysis or impaired bladder and bowel control ( urinary incontinence and fecal incontinence). Sometimes these problems can... read more .)
The human T-lymphotropic virus 1 (HTLV-1) is similar to the human immunodeficiency virus Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and can cause acquired immunodeficiency syndrome (AIDS). HIV is transmitted... read more 
(HIV), the virus that causes AIDS. The HTLV-1 virus can cause certain kinds of leukemia Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more and lymphoma Overview of Lymphoma Lymphomas are cancers of lymphocytes, which reside in the lymphatic system and in blood-forming organs. Lymphomas are cancers of a specific type of white blood cells known as lymphocytes. These... read more 
(cancers of the white blood cells).
HTLV-1 is transmitted through
Sexual contact
Use of illegal drugs that are injected into vein (intravenously)
Exposure to blood
It can be transmitted from mother to child through breastfeeding. It is most common among prostitutes, injected drug users, people undergoing hemodialysis, and people from certain areas such as those near the equator, southern Japan, and parts of South America.
Tropical spastic paraparesis/HTLV-1–associated myelopathy is more common among women because HTLV-1 infection is more common among women.
A similar disorder can result from infection with a similar virus, human T-lymphotropic virus 2 (HTLV-2).
The virus resides in white blood cells. Because the cerebrospinal fluid contains white blood cells, the spinal cord can be damaged. Inflammation develops in the spinal cord and damages the pathways that carry signals about pain, temperature, and position up the spinal cord to the brain and those that carry signals from the brain down the spinal cord to muscles. Damage to the spinal cord results more from the body’s reaction to the virus than from the virus itself.
Symptoms
The muscles in both legs gradually become weak. People may not be able to feel vibrations in their feet and may lose the sense of where their feet and toes are (position sense). Their limbs feel stiff, movements become clumsy, and walking may become difficult. Muscle spasms in the legs are common, as is loss of bladder control (urinary incontinence Urinary Incontinence in Adults Urinary incontinence is involuntary loss of urine. Incontinence can occur in both men and women at any age, but it is more common among women and older people, affecting about 30% of older women... read more 
) and urinary urgency (an urgent need to urinate).
Tropical spastic paraparesis/HTLV-1–associated myelopathy usually progresses over several years.
Diagnosis
Assessment of the person's risk of being exposed
Magnetic resonance imaging
Tests to check for the virus in blood and cerebrospinal fluid
The diagnosis of tropical spastic paraparesis/HTLV-1–associated myelopathy is usually based on symptoms and the person’s risk of being exposed to the virus. Thus, a doctor may ask people about their sexual contacts and use of illegal injected drugs.
Samples of blood and cerebrospinal fluid, obtained by a spinal tap Spinal Tap 
(lumbar puncture), are tested for parts of the virus or antibodies to the virus. (Antibodies are produced by the immune system to defend against a particular attacker, such as HTLV-1.)
Magnetic resonance imaging (MRI) of the brain and spinal cord is done to check for abnormalities such as degeneration of the spinal cord and to check for other possible causes of the symptoms.
Treatment
Interferon alfa, immune globulin, and/or corticosteroids
For spasms, muscle relaxants
No treatment has been shown to be effective for tropical spastic paraparesis/HTLV-1–associated myelopathy. However, interferon alfa (an antiviral drug), intravenous immune globulin Immune globulins A virus is composed of nucleic acid, either DNA or RNA, surrounded by a protein coat. It requires a living cell in which to multiply. A viral infection can lead to a spectrum of symptoms from... read more , and/or corticosteroids may slow the progression of the disorder and reduce disability and pain. (Intravenous immune globulin is a purified solution of antibodies obtained from volunteer donors and given by vein.)
Spasms can be treated with muscle relaxants such as baclofen or tizanidine.
