Craniofacial Muscles

82 F. Pedrosa Domellöf
adhesions between adjacent palpebral and orbital structures. In a subgroup of
patients, the progressive increase in orbital tissue volume pushes the eye forward, a
condition termed exophthalmos or proptosis. Increased orbital volume imposes
mechanical constraints for the action of the EOMs. However, the most feared aspect
of TAO is compression of the optic nerve due to increased intraorbital pressure, as
it is may compromise vision irreversibly.
Diplopia has been reported to occur in approximately 20% of the patients who
develop TAO. Blurred vision, which may have different etiologies including discretely
disturbed eye motility, occurs in approximately 10% of patients with TAO
(Bartley et al. 1996 ) . The involvement of the EOMs in TAO may vary, from rather
discrete and not readily apparent from a clinical examination, to extensive fi brotic
restriction of eye movements. Imaging techniques such as CT and MRI are very
helpful for identifying and quantifying the extent of EOM involvement, whereas
velocity measurements of saccadic eye movements have, thus far, provided controversial
results and are not easy to use in a clinical setting (Träisk 2009 ) .
At the tissue level, the changes behind TAO include expansion of orbital connective
and fat tissue, in fi ltration of orbital tissues, including the EOMs, with mononuclear
cells and hyaluronan, and, in the long run, fi brosis and impaired eye motility
(Khoo and Bahn 2007 ) . The orbital fi broblasts are regarded as major players in
these processes, particularly regarding adipogenesis, and data indicate that they are
the primary targets in the orbit for the circulating autoantibodies against thyrotropin
receptor. Autoantibodies against insulin-like growth factor-1 (IGF-1) also play an
important role in recruitment and activation of T-cells and stimulation of hyaluronan
deposition. Deposition of hyaluronan in between muscle fi bers and in fatty
connective tissue leads to increased volume of the EOMs and orbital contents but
the process underlying TAO also includes in fl ammation and damage of the EOMs,
re fl ected by the presence of detectable autoantibodies against these muscles (Khoo
and Bahn 2007 ) .
5.7 Amyotrophic Lateral Sclerosis
ALS is a progressive, fatal, neurodegenerative syndrome affecting both the upper
and lower motor neurons and their supporting cells (Boillée et al. 2006 ; Andersen
2006 ) . It is clinically characterized by progressive loss of voluntary muscle function,
leading to early death due to respiratory failure. The incidence of ALS increases
with age, and it typically affects people in the sixth decade or older. The disease
may have a bulbar onset in 20–25% of the patients with initial symptoms of dysphagia
and dysarthria. However, a systemic onset, usually in a limb muscle, is more
common; the cranially innervated muscles are also involved at later stages. Strikingly,
involvement of the EOMs is not a typical feature of ALS, although it does occur in
some cases, particularly in patients who survived longer periods due to assisted
ventilation (Leveille et al. 1982 ; Hayashi et al. 1987 ; Palmowski et al. 1995 ) . Human
EOMs of donors who died of ALS without ventilator support show mild signs of