Rare autoimmune muscle disease identified

Evelyn Lewin

30/04/2019 12:31:12 PM

The syndrome causes sudden onset of debilitating muscle pain, along with moderate to severe progressive weakness.

Man with sore knee
The disease affects proximal muscles symmetrically, causing pain and weakness.

Described in the latest issue of Neurology, large histiocyte-associated myopathy (LHIM) has been identified in a total of four patients.
All patients identified had anaemia and high serum creatine kinase (CK) levels, ranging from 10,000–102,000 U/L, as well as proximal, symmetric, moderate to severe weakness in the arms and legs, progressing over one to four weeks.
Histologically, all patients showed a distinctive pattern of large histiocyte-associated muscle fibre necrosis. Of the four patients identified with LHIM, three were treated with immunomodulating therapy, such as steroids.
All three of those patients improved within three months of treatment, and have not since relapsed. The fourth patient was undergoing cancer treatment when he developed muscular symptoms and died from cancer shortly after.
The senior author of this new paper, Dr Alan Pestronk, a professor of neurology, pathology and immunology, notes that having identified only four patients with the condition makes the disease ‘very rare’.
However, he believes it is important for doctors to know about it.
‘It has never been described before, and it seems to be treatable, so it will be helpful for physicians to be aware of it,’ he said.
‘People don’t need to be afraid this is going to happen to them, but in the extremely rare event that it does, physicians should now have the tools to respond.’
Dr Pestronk identified the first patient with what is now known as LHIM, back in 1996.
At that time, he was reviewing microscope slides of muscles from a patient with muscle pain and weakness when he discovered scavenger cells – which normally feed on dead material – crowding around injured muscle fibres.
‘This was an unusual enough situation that I kept it in my memory and stayed on the lookout for other cases like this,’ Dr Pestronk said.
Over the next 22 years, he came across three more patients hospitalised for muscle pain and weakness, whose biopsies also showed muscle breakdown with scavenger cells.
Analysing the biopsies led Dr Pestronk and his colleagues to discover that the patients’ own muscles were under assault by immune scavenger cells, known as histiocytes.
Dr Pestronk said understanding how muscle fibres are damaged by immune cells could help prevent such damage.
‘There are several immune muscle diseases where the primary damage you see under the microscope is muscle fibre breakdown. Each of those diseases has a different prognosis and requires a different treatment,’ Dr Pestronk said.
‘Physicians need to recognise the immune nature of this condition in order to treat it appropriately.’
LHIM has a similar presentation to rhabdomyolysis and generates similar results on blood chemistry work-up, such as elevated CK levels.
However, treatment of rhabdomyolysis involves intravenous fluids (along with dialysis in some cases), while LHIM requires treatment with immunomodulating therapy.
According to the Australasian Society of Clinical Immunology and Allergy (ASCIA), there are over 80 different autoimmune diseases, ranging from common to very rare. ASCIA reports that autoimmune diseases affect around 5% of people.

autoimmune disease LHIM muscle pain muscle weakness myopathy

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