The Primary aHUS community now understands that there is no accurate record of how many “aHUS” patients there are , but what about the number of people who have had TMAs?
It is no surprise to find there are no records either for this medical emergency which is akin to a heart attack or stroke. Yet less is known about TMA. It must be rare too.
In articles about TMAs there is rarely any mention of their incidence or prevalence rates of patients numbers.
A regular answer to an internet search for “TMA incidence” rate is “1 to 3 per million”. That would mean there are about 340 to 1020 TMA incidents in the USA each year. There are no estimates for TMA prevalence but only broad statements that it is higher, which is obvious.
The incidence of Primary aHUS, or the complement mediated version of aHUS, in the USA is estimated to be 1 per 2 million or about 170 new cases per year.
If the internet TMA estimate is to be believed then 50%, at the lower end, to 16% , at the higher end , of TMA cases are aHUS.
If that was true there would be much less difficulty in diagnosing complement mediated-aHUS TMAs among all TMA manifestations.
A toss of the coin would be as accurate at the lower estimate of all TMA incidence.
The report that made the proposal to change aHUS nomenclature to a host of TMA rooted disease names makes no attempt to say how many TMA patients will be impacted by the change because they have no idea of the current global TMA footprint.
Let alone any notion if all will be changed at the end of it or whether they have been changed correctly. The devil, as they say, will be in the detail.
What has Global Action found about TMA patient numbers.
Well only that it is said frequently that there are more female TMA patients than male patients. Slightly higher ratio than usually reported in “aHUS” . Roughly 3F:1M in all TMAs whilst 2F:1M in Primary aHUS.
French researchers have probably done the most to elucidate the numbers of TMAs falling into the different categories of Primary TMA and Secondary TMAs.
Three studies have looked at the number of TMA patients diagnosed over the years in French Hospitals.
Two studies of cities in France , Tours and Angers attempted to categorise the TMA cases admitted to their hospitals over 9 and 11 years respectively.
Global Action has featured the Bayer group’s study of 564 adult TMA patients in Tours before.
Over an 9 year period, hospitals in the city of Tours (population 1 million) were found to have 3 “aHUS” incident patients out of every 100 diagnosed all age cases of TMA.
Primary TMAs (just TTP and aHUS in this group’s definition) ) totalled 6 % of all the TMAs. Secondary TMAs, which included typical HUS, represented 94%. So roughly 15 Secondary TMAs for every 1 narrowly defined Primary TMA case.
Adding in typical HUS patients to Primary TMA numbers the Primary TMA percentage would be 12%.
Overall there would be 30 “other” TMAs for every “aHUS” case.
In a study of 216 adult TMA cases in a hospital in Angers in Western France there were 8 patients identified as having “aHUS” over a 11 year period.
There were 20 Primary TMA patients, which in the Angers’ study again included TTP and aHUS only. So not including typical HUS. These Primary TMA patients were just under 10% of all TMA patients. If the typical HUS patients were included in the Primary TMA numbers the percent would be 13%. So not too different from what was found in Tours. Secondary TMAs far out number Primary TMAs . Even more so than what is regarded as “aHUS”.
A recently published third French adult patient study which looks at TMAs is not strictly about the condition’s etiology (patient numbers) but about its diagnosis. or more specifically diagnosis confirmation by biopsy.
It excludes all TMA patients who did not get a biopsy to confirm of having a TMA. The 53% male cohort in this study shows that many TMAs in female patients due to pregnancy did not need biopsies. Nor did some TTP or HUS patients identified by ADAMTS13 and E.coli tests.
It is large study of 967 adults’ diagnoses in 25 French hospitals which were confirmed by biopsy over 14 years.
What is interesting among all the usual categories of TMA, cancer , drugs, bone marrow transplant etc , this group’s study uses the categories aHUS and C-HUS (complement mediated HUS too).
It claims that nearly 50% these TMAs were due to aHUS (41.6%) and C-HUS (7.6%).
This shows the nomenclature creep that exists in research articles and how the Primary HUS and Secondary HUS classifications have clouded the picture. C-HUS is the Primary HUS or original aHUS which seeded the many “aHUS” dominated patient communities which exist to day.
So what might be learned from these studies:
- that the prevalence of TMA patients is more than 1 to 3 per million and is probably more like 30per million , but it still would be rare;
- there are many more Secondary TMAs than Primary TMAs ( however they are defined, French researchers do not regard typical HUS as a Primary TMA) ;
- TMAs affect women more than men by as much as 3 to 1;
- pregnancy dominates as a cause of a TMA;
- if the bulk of the pregnancy TMAs are excluded, then for other TMAs it might be more like 50:50, men v women;
- the incidence of TMAs in child patients would alter these ratios and percentages, as TMA causes are more diverse in adults than they are in children. Though probably increasing the Secondary TMAs because of the preponderance of typical HUS TMA incidents in children
- Primary aHUS occurs in 3 to 4% of TMA cases, marginally lower than either TTP or typical HUS
- The relative all age incidence of Primary aHUS and typical HUS is nothing like level from which an aHUS prevalence rate of 2 per million was derived more than 25 years ago.
Article No. 723
