Patients with pheo often ask “why
do I have pheo?” I usually assure them that nothing we know of, other than
genetic risks, causes pheo. There is no clear evidence that common risk factors
such as smoking, obesity, diet, infection, and exposure to environmental toxins
are associated with higher pheo risk. There is also no clear evidence that
other diseases the patient has, other than those that are part of a genetic
syndrome, are associated with higher pheo risk.
An interesting paper published
online last month seems to suggest that cyanotic congenital heart diseases may
predispose people to develop pheo. The idea that hypoxia may lead to pheo is
not too new now. About half of the genes that cause pheos when mutated are
involved in making molecules carrying energy. As making energy molecules
requires oxygen, the mutated genes mislead the cell into thinking that it lacks
oxygen supply (hypoxia). The cellular processes that try to cope with hypoxia,
over time, can result in pheos. It has been reported that people living in high
altitude (thus low oxygen levels) tend to have more neck paras and perhaps pheos.
The new paper now shows that people with cyanotic congenital heart disease may also
tend to have more pheos.
Cyanotic congenital heart
disease is a congenital condition in which the abnormal heart structure causes
mixing of blood from the two sides of heart, thus low oxygen levels in the
artery and tissue. The new paper shows that people with cyanotic congenital
heart disease have a 6-fold risk of having a pheo diagnosis, compared with
those without, during their hospitalization for whatever causes. In the same
paper, the authors also identified 20 patients with congenital heart disease
and pheo, 18 of them having cyanotic disease, 2 having aortic coarctation. The
18 patients with cyanotic congenital heart disease were younger than the average
patients with pheo and tend to have multiple tumors. Unfortunately, the paper
does not specify the 18 patients were out of how many patients with cyanotic
congenital heart disease so that we don’t know the incidence of pheo in those
patients.
As the authors prudently
cautioned, their study only establishes an association between pheo and cyanotic
congenital heart disease but not a causal effect of chronic cyanosis. One other
potential bias is from ascertainment. If more patients with cyanotic congenital
heart disease are tested for pheo, more pheos will be diagnosed. Nonetheless, I
will ask my next patient with suspected pheo whether she/he has a history of
congenital heart disease, especially a cyanotic one.
Dr. Pheo
