Page 7 - 2020 Spring CMTA Report

HEREDITARY NEUROPATHY WITH LIABILITY

TO PRESSURE PALSIES EXPLAINED

BY JUN LI, MD, PHD

erve tissues that reside in the While exceptions do occur, patients with HNPP may experi-
skull and spinal canal make the majority of patients with ence permanent weakness. Some
up the central nervous HNPP develop initial symptoms episodes may not have any identi-
system (CNS). The nerve around the first or second decade fiable triggers.
Nfibers outside of the CNS of life. Patients typically present Peripheral nerves that go to
are collectively called peripheral with focal numbness, tingling muscles and sensory organs in the
nerves. When the peripheral (pins/needles) and muscular weak- head are called cranial nerves and
nerves are damaged by a cause, ness in limbs. These episodes are can also be impacted by HNPP.
it is called peripheral neuropathy. often brought on by mild physical For instance, partial hearing loss
If the cause is a genetic and facial numbness have
mutation in a specific been reported by patients
gene, it is called Charcot- with HNPP. Many patients
Dr. Li is a professor
Marie-Tooth disease with HNPP also develop
and chairman of the
(CMT). More than 100 generalized symptoms such Department of Neu-
gene mutations that as intolerable fatigue and rology at Wayne State
cause CMT have been pain. There is a wide range University School of
identified—hereditary in the severity of these Medicine and Detroit
Medical Center.
neuropathy with liability symptoms. Life expectancy
He is a member of
to pressure palsies (HNPP) for people with HNPP is the CMTA’s STAR
is one of them. usually not affected by the Advisory Board.
No one knows the disease.
true prevalence of HNPP Some patients may be
patients. Genetically, it is Episodes are asymptomatic, which can
a reciprocal disease of lead to severe limb paralysis
CMT1A, thus it should often brought on when they participate in
have a prevalence similar by mild physical strenuous physical activities
to CMT1A. However, due activities that like running 10 miles a day
to the difficulties in diag- do not cause with a 50-pound backpack.
nosing HNPP, the true One asymptomatic woman
HNPP prevalence has not symptoms in developed leg paralysis after
been well documented. healthy people. a nine-hour labor spent sit-
HNPP is caused by a ting in birthing position.
missing DNA segment on The diagnosis of
chromosome 17. The seg- HNPP can be quite chal-
ment—c17p12—contains the activities that do not cause lenging, due in part to many
PMP22 gene, among others. Loss symptoms in healthy people. physicians’ unfamiliarity with the
of one of the two copies of the The activities include compression disease. Upon physical examina-
PMP22 gene (one from mother from sitting with legs crossed, tion, physicians may find
and one from father) is responsi- putting pressure on the peroneal sensation loss and muscle weak-
ble for HNPP, which means that nerve, or leaning on elbows ness in the hands and feet. Unlike
HNPP has a 50 percent chance against the ulnar nerve; repetitively other types of CMT, high arching
of being passed to offspring. A doing the same movements feet or hammer toes are not com-
small fraction of patients with (stereotypic movements) for a pro- mon in patients with HNPP. An
HNPP may develop this muta- longed period; and over-stretching HNPP patient may be misdiag-
tion on their own, which is called of the arms or legs. It can take nosed with a lacunar stroke,
de novo mutation, and thus anywhere from hours to months multiple sclerosis, spinal muscular
would not have any family his- to recover from an episode. While atrophy, chronic inflammatory
tory of the disease. most episodes are transient, some (continued on page 12)

SPRING 2020 THE CMTA REPORT 7