HTLV-1 Associated Myelopathy (HAM) is a slowly progressive, chronic disease of the spinal cord seen in some people infected with the HTLV-1 virus, which results in painful stiffness and weakness of the legs. HAM is also referred to as chronic progressive myelopathy or tropical spastic paraparesis (TSP).
An estimated 5-20 million people in the world are infected with HTLV-1. Although the HTLV-1 virus is present throughout the world, infection with the virus is endemic in some geographical areas — the Caribbean, southern Japan, areas of Africa that are near the equator, and the Seychelles. Other areas that have a high rate of infection include Central and South America, Melanesia and southern Africa.
The HTLV-1 virus is transmitted (passed) from an infected person to a non-infected person through bodily secretions and blood.
- It can be transmitted by sexual contact, via the blood through fresh blood transfusions or through re-use of contaminated needles or passed from mother to child through breast-feeding.
- You cannot spread HTLV-1 by casual contact, such as shaking hands, hugging, and sharing homes and workplace, including bathrooms.
- The transmission of the virus can be decreased through safe sex practices (i.e. condoms or abstinence from intercourse) and avoiding needle sharing.
- Women who test positive for the virus should not breast feed.
- Healthcare practitioners should use caution when handling sharp instruments or handling bodily secretions from an infected person.
The great majority people who test positive for the HTLV-1 virus do not go on to get active disease; these individuals are called carriers.
Who gets HAM/TSP, and when?
Of the 5-20 million people infected with the HTLV-1 virus worldwide, approximately 0.25 to 3 percent of the infected individuals will develop HAM/TSP. (An additional two percent of people infected with the HTLV-1 virus will develop a serious blood cancer (adult T-cell leukemia or lymphoma).) The great majority of individuals infected with the HTLV-1 virus will never exhibit signs or symptoms of disease.
However, in some people who are infected with the HTLV-1 virus, inflammation (swelling) occurs in the spinal cord; the immune system's attack on the virus involves sending cells called lymphocytes to the affected area. These lymphocytes release chemicals called cytokines, which not only kill the infected cells but can also cause damage to the nerves. When the immune system's response to the virus causes nerve damage in the spinal cord, the legs gradually lose strength and flexibility.
The symptoms of HAM/TSP usually appear between the ages of 30 and 50 but may occur earlier. The disease has been known to appear in childhood, but this is very rare. The disease may remain undetected for years after infection begins but can still be transmitted to another person during this time.
How is HAM/TSP different from MS?
Many of the symptoms of HAM/TSP are also found in people who have been diagnosed with MS. The clinical course of HAM/TSP is most similar to the primary-progressive form of MS (PPMS) in that there is a steady worsening of neurologic functioning without any distinct relapses (also called attacks) or periods of remission.
Reviewed by Elias Sotirchos, MD November 2019