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The odds of being infected with HTLV-1 are slightly higher than the odds of developing multiple sclerosis when looking at worldwide statistics. However, when you consider how few carriers of the infection actually develop HAM, it’s a very rare condition.

A number of diseases can be mistaken for multiple sclerosis. That’s partly because MS has so many symptoms, and those symptoms manifest inconsistently from one patient to another, making each case unique.

In addition, MS is far from the only disease or condition that directly affects the central nervous system, or CNS. This makes diagnosing multiple sclerosis difficult, especially since so few people even know of some of the potential diseases that could cause the same symptoms.

HTLV-1 Associated Myelopathy, or HAM, is one such disease. HTLV-1 is a very old disease that has been around for hundreds of years, and it’s estimated that somewhere around 20 million people have HTLV-1, with most not even knowing it because it is asymptomatic in so many cases. However, when it leads to HAM, it can look a lot like multiple sclerosis on the first pass.

What is HTLV-1 associated myelopathy?

First, it’s important to understand that HTLV stands for Human T-cell Leukemia Virus, which infects the T-lymphocytes (a type of white blood cell). For most people carrying the virus, there are no consequences, though about one in five will eventually develop a disease related to it, such as HAM, typically decades after being infected. Less than three percent of people with HTLV-1 develop HAM.

HAM, which is often grouped with TSP or Tropical Spastic Paraparesis, is one such disease that can come with the territory of infection by HTLV-1. HAM causes swelling in the brain and spinal cord that can damage the nervous system and lead to symptoms that appear almost identical in some ways to multiple sclerosis.

HAM vs MS: Symptoms and similarities

Unlike some other diseases that mimic multiple sclerosis, HAM doesn’t manifest similarly to relapsing-remitting MS. Instead, it presents like the more serious primary progressive MS, in which patients have a sudden, extreme onset of symptoms that never go into remission. Both diseases are typically diagnosed later in life, when patients are in their late forties and fifties, but they can be diagnosed at any age. They are both progressive, chronic diseases that can cause degeneration and affect the central nervous system.

Other similarities include:

  • Pain, stiffness, and weakness in the legs and, perhaps, throughout the body
  • Difficulty standing from a chair or climbing stairs and problems with gait
  • Bladder issues, such as incontinence, inability to empty the bladder, urgency to urinate, and increased trips to the bathroom
  • Tingling and numbness in feet or extremities
  • Double vision
  • Tremors and spasm
  • Inflammation of the central nervous system (CNS)
  • Rapid progression of the disease, with symptoms worsening quickly
  • The use of a similar battery of tests for diagnosis that include:
    • Blood tests for certain antibodies and to rule out other conditions
    • Spinal tap/lumbar puncture to test for antibodies
    • MRI of the brain and spinal cord to look for inflammation and lesions
    • EP (evoked potential) testing to monitor brain activity when certain stimulation is applied to nerves
  • In both diseases, women are at a higher risk than men of development (twice as likely to develop HAM and three times as likely to develop MS)

While on the surface, the two chronic conditions are quite similar in presentation, there are plenty of differences to set them apart as well.

Conditions and differences

Multiple sclerosis is an autoimmune disease, the cause of which is unknown, caused when the immune system attacks the myelin, or protective coating, on the nerves in the CNS, which also help speed up the function of messaging through the nervous system. This causes destruction of myelin and, eventually, the nerves. HTLV-1 is a retroviral disease that is transmitted through sexual contact without a condom, sharing used needles, and breastfeeding by an infected mother. HAM does not occur without the initial infection.

Other differences also abound:

  • HTLV-1 can be “dormant” in a carrier for decades prior to the onset of HAM, while multiple sclerosis is a sudden onset of symptoms when the immune system first launches an attack.
  • Multiple sclerosis is not a communicable disease. While HTLV-1 is not “airborne”, and it cannot be contracted by being in the same space as, shaking hands with or hugging, or using the same bathroom as an infected person, it can be transmitted between people through bodily fluid exchange.
  • Multiple sclerosis is most common in people of Caucasian, European descent and occurs more frequently in areas with temperate climates (cooler temperatures and less sunlight). Alternately, HAM is more prevalent in the Caribbean, southern Japan, the southern regions of Africa, the Middle East, South America, and Melanesia, as well as in people with ancestry in these regions.
  • Though the initial onset of HAM typically appears as significant progression of the disease, after the first two to three years, this slows significantly. In the vast majority of cases, it takes decades to develop disabilities related to the disease, and it is almost never fatal. With the right therapy, most patients can live normally. With the more common relapsing-remitting MS, symptoms come and go and take years to significantly progress. Even in primary progressive MS, symptoms tend to worsen at a steady pace, though that pace never seems to slow.


The odds of being infected with HTLV-1 are slightly higher than the odds of developing multiple sclerosis when looking at worldwide statistics. However, when you consider how few carriers of the infection actually develop HAM, it’s a very rare condition. And comparing the demographics, it’s even rarer in North America. However, treatment for the disease will help patients live a fuller, happier life.

With multiple sclerosis, treatment can help prolong periods of remission between relapses and slow the progression of the disease. It can also help manage symptoms for a better quality of life. Even with primary progressive MS, treatment can afford some relief and reduce the instance of disability.

With either disease, the first step is speaking to a physician to get a diagnosis. Ruling out all other possibilities so a focus on the existing ailment can be official will start patients down the right path for the best chance of management and comfort for the rest of their lives.

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