Rchahilitacija - Letnik VII. .111p/ . -/ ! 2008) 
ELECTROMYOGRAPHY OF THE 
DIAPHRAGM ANO PHRENIC NERVE 
CONDUCTION STUD/ES IN PATIENTS 
WITHALS 
S. Podnar. l. Rigler
Institute of Clinical Ne urophysiology. University Medical Ce ntre Ljubljana. Ljubljana. Slovenia
In patients with restrictive ventilation failure of unknown 
aetiology neuromuscular disorders always need to be con­
sidered. In suspected lesions to the phrenic anterior horn 
neuro ns or motor axons or to the diaphragm electrodiag­
nostic investigation, including phrenic nerve conduction 
studies and needle examination of the diaphragm muscle, 
can be useful. Phrenic nerve conduction studies are usually 
done using a supramaximal (80-100 mA, 0.1-0.2 ms long) 
electrical stimulation applied by a surface electrodes in the 
supraclavicular fossa (just above the clavicle, between both 
heads of the sternocleidomastoid (SCM) muscle) ( 1 ), and 
with a pair of self adhesive recording electrodes on the thorax 
(the active electrode (G 1 ): 5 cm above the xiphoid process, 
the reference electrode (G2): 16 cm f
r
om G 1, on the chest 
margin (2)). Phrenic nerve M-wave parameters describing 
axonal loss (amplitude (mY), and area (mYms)), or demy­
elination (latency and duration and (ms)) can be measured. 
Needle examination of the diaphragm muscle is usually 
done by a standard concentric EMG needle inserted into thc 
mcdial recess of the 7
th
, 8
th 
or 9
th 
intercostal space (3). During 
slow advancement of the needle electrode through the tissue 
EMG signal is carefully observed and listened. Rhythmic 
bursts of low amplitude MUPs during inspirations disclose 
that tip of the electrode reached the diaphragm (3). At that 
point EMG activity during normal breathing is obscrved. 
In addition, motor unit potential (MUP) parameters can be 
measured (quantitative MUP analysis), and compared to 
normative limits ( 1 ). 
Respiratory electrodiagnostic studies are valuable also in 
paticnts with suspected ALS, because some ofthese patients 
present with respiratory insufficiency. Furthermore, respira­
tory failure limits the life span of these patients. However, 
in this population apart from lower motor neuron (at high 
cervical or thoracic levels) upper motor neuron involvement 
may cause of respiratory failure. Phrenic nerve conduction 
studies and needle examination of the diaphragm muscle, 
however, evaluate mainly only the lower motor neuron func­
tion. Low amplitude or area of the phrenic nerve M-wave 
point to few remaining functional diaphragm muscle fibres, 
and therefore to a advanced stage of the disease in the res­
piratory domain. The needle EMG studies may be of some 
prognostic value and aid in long-term planning of respiratory 
management in patients with ALS. Abundant spontaneous 
denervation activity with a decreased number of relatively 
normal-sized MUPs points to acute denervation and rapidly 
developing disease with poor reinnervation. In contrast, little 
spontaneous denervation activity with a decreased number 
of large MUPs indicates a more slowly progressive denerva­
tion and better reinervation. Respiratory electrodiagnostic 
findings need to be combined with electrodiagnostic find­
ings obtained in other trunk and limb nerves and muscles 
to diagnose ALS. 
Reference s: 
l. Resman-Gaspcršič A, Podnar S. Phrenic ncrve con­
duction studies: technical aspects and normative data.
Muscle Nerve 2008; 37: 36-41.
2. Chen R, Collins S, Remtulla H, Parkes A, Bolton CF.
Phrenic nerve conduction study in normal subjects.
Muscle Nerve 1995; 18: 330-5.
3. Bolton CF, Grand'Maison F, Parkes A, Shkrum M. Ncc­
dle electromyography of the diaphragm. Musclc Nerve
1992; 15: 678-81.
m