Baylor University Medical Center Proceedings July 2017 - 331

MG symptoms (12). Recent
studies suggest that thymic
carcinoma patients with
paraneoplastic MG have a
signiﬁcantly better prognosis
of cancer survival (13). These
patients' increased survival is
likely due to higher resection
rates from smaller size and
earlier stage of the primary
tumor (13).
Our patient's presentation
of MG was interesting,
c
d
as he did not have symptoms of MG when he had
the primary thymic cancer
in 2006. After thymectomy,
recurrence and metastasis of
his malignant thymoma were
accompanied by MG symptoms. A classical presentation of MG was seen when
tapering steroids for rash
and respiratory complaints,
Figure 1. Photomicrographs of the mediastinal mass recurrence diagnosed via core biopsy showing (a) discrete sheets of which could have masked
cells within a fibrous background (20×) and (b) large epithelioid cells with occasional nucleoli and indistinct cell borders MG symptoms. It was inter(200×). Only scattered small lymphocytes were present. (c) PAX-8 immunohistochemistry highlights the epithelioid cells. esting that the patient devel(d) TdT immunohistochemistry highlights scattered immature thymic T-lymphocytes. Combined positive PAX-8 and TdT oped MG symptoms when
immunohistochemical stains help support the diagnosis of a thymic tumor. (Histologic slides of the original resection from his underlying cancer was
2006 were not available for comparison.)
responding to chemotherapy.
Most of the metastases are to
the lymph nodes, liver, and soft tissue/skeletal muscles, and this
exhibits aggressive clinical behavior, atypical cytology, and poor
patient's metastasis to the C7 vertebra was unusual.
prognosis (5). Both thymoma and thymic carcinoma may inPlasmapheresis or intravenous immunoglobulin can be benvade surrounding tissue such as the mediastinum, pericardium,
eﬁcial for severe symptoms of MG (14). Our patient showed
and pleura. The main distinction between thymoma and thymic
drastic symptomatic improvement after undergoing ﬁve rounds
carcinoma is the histologic atypia seen in thymic carcinoma,
of plasmapheresis. Moderate MG symptom improvement has
which can demonstrate multiple histologic cell types (7). When
been reported with removal of thymic carcinoma metastases
a thymoma behaves aggressively with invasion, it is sometimes
to the pleura (8). Unfortunately, our patient was not a surgical
termed malignant (or invasive) thymoma (6). A small biopsy
candidate due to multiple extrathoracic metastases.
cannot adequately demonstrate the mixed histology that can
be present. Metastasis from thymic tumors is most commonly
1. Akaishi T, Suzuki Y, Imai T, Tsuda E, Minami N, Nagane Y, Uzawa A,
seen in lymph nodes, liver, and soft tissue/skeletal muscles, with
Kawaquchi N, Masuda M, Konno S, Suzuki H, Murai H, Aoki M,
other sites including bone, brain, and abdominal wall (8-11).
Utsugisawa K. Response to treatment of myasthenia gravis according to
Thymic neoplasms can be associated with various paraclinical subtype. BMC Neurol 2016;16(1):225.
neoplastic syndromes including MG (7). Common symptoms
2. Querol L, Illa I. Myasthenia gravis and the neuromuscular junction. Curr
associated with MG are diplopia, extraocular muscle weakOpin Neurol 2013;26(5):459-465.
3. Gilhus NE, Verschuuren JJ. Myasthenia gravis: subgroup classiﬁcation
ness, ptosis, limb weakness, and, in severe cases, respiratory
and therapeutic strategies. Lancet Neurol 2015;14(10):1023-1036.
distress (2, 3). Five subtypes of MG have been characterized:
4. Nakajima J, Okumura M, Yano M, Date H, Onuki T, Haniuda M,
ocular, hyperplastic thymus, thymoma associated, AchR-Ab
Sano Y, Yoshino I, Asamura H, Yoshida K, Nagai K, Yokoi K, Miyoshi S,
negative, and AchR-Ab positive without thymic abnormaliHigashiyama M, Suzuki K, Tsuchida M, Haraguchi S, Niwa H, Kondo K,
ties (1). Rare extrathoracic metastases of malignant thymoma
Horio H, Matsumura A, Okamoto T, Ikeda N, Maniwa Y, Onuki T, Suzuki
M, Nagayasu T, Iwasaki A, Suehisa H, Ohde Y, Kondo K; Japanese Asso(e.g., liver, bone) have also been associated with a few cases
ciation for Research of Thymus. Myasthenia gravis with thymic epithelial
of MG (9-11).
tumour: a retrospective analysis of a Japanese database. Eur J Cardiothorac
In patients with thymoma-associated MG, thymectomy
Surg 2016;49(5):1510-1515.
in conjunction with acetylcholinesterase inhibitors (such as
5. Mikhail M, Mekhail Y, Mekhail T. Thymic neoplasms: a clinical update.
pyridostigmine) usually results in minimal manifestation of
Curr Oncol Rep 2012;14(4):350-358.
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