18-fluorodeoxyglucose ( fdg ) uptake in muscles , in positron emission tomography - computed tomography ( pet / ct ) scan can be attributed to voluntary muscle activity such as talking , chewing , exercise or involuntary muscle activity like labored breathing or stress induced muscle spasms .
we describe an interesting pattern of fdg uptake in muscles in a case of the right lung malignancy .
a 36-year - old indian male , underwent whole body fdg pet / ct for staging of recently diagnosed right lung carcinoma .
the pet / ct scan showed increased fdg uptake in right perihilar lung lesion [ black arrow in figure 1a and red arrows in figure 1b ] compatible with known lung neoplasm .
there was no abnormal fdg uptake in the mediastinal lymph nodes . maximum intensity projection image also showed increased fdg uptake in accessory muscles of respiration - bilateral sternocleidomastoid and inter coastal muscles [ blue arrows in figure 1a ] and unilateral , intense fdg uptake in left hemi - diaphragm [ red arrows in figure 1a and c ] .
on ct , there was no morphological abnormality in any of the above - mentioned muscles with fdg uptake .
coronal ct image revealed elevated right hemi - diaphragm [ arrow in figure 2a ] , suggestive of right diaphragmatic paralysis .
fused pet / ct image [ coronal slice , arrow in figure 2b ] , shows intense fdg uptake in left hemi - diaphragm .
the maximum standardized uptake value of this uptake was 6.1 ( normalized for body surface area ) .
these fdg pet / ct findings suggested a cause - effect relationship , indicating right phrenic nerve palsy caused by the lung neoplasm resulting in right diaphragmatic paralysis .
this possibly resulted in asymmetric , intense fdg uptake in the left hemidiaphragm and accessory muscles of respiration , due to compensatory increased workload related to contralateral right diaphragmatic paresis .
the positron emission tomography / computed tomography scan of a young male , showed increased fluorodeoxyglucose ( fdg ) uptake in right perihilar lung lesion [ black arrow in figure 1a and red arrows in figure 1b ] compatible with known lung neoplasm .
maximum intensity projection image also showed increased fdg uptake in accessory muscles of respiration - bilateral sternocleidomastoid and intercoastal muscles [ blue arrows in figure 1a ] and unilateral , intense fdg uptake in left hemi - diaphragm [ red arrows in figure 1a and c ] .
on ct , there was no morphological abnormality in any of the above - mentioned muscles with fdg uptake coronal computed tomography ( ct ) image revealed elevated right hemi - diaphragm [ arrow in figure 2a ] , suggestive of right diaphragmatic paralysis .
fused positron emission tomography / ct image [ coronal slice , arrow in figure 2b ] , shows intense fluorodeoxyglucose uptake in left hemi - diaphragm .
the maximum standardized uptake value of this uptake was 6.1 ( normalized for body surface area )
muscle fdg uptake can be attributed to voluntary or involuntary muscle activity , increased insulin , surgical interventions and inflammatory conditions affecting muscles .
focal fdg uptake in muscles can also be seen in primary muscle neoplasm or metastatic involvement , however in these cases morphologic abnormality may be seen in the corresponding ct images .
increased fdg uptake in accessory muscles of respiration and bilateral diaphragmatic muscles is known to occur in patients with labored breathing or coughing . in our case , prominent fdg uptake in unilateral diaphragm ( left diaphragm ) and bilateral accessory muscles of respiration was noted .
this paresis appears to be the result of phrenic nerve palsy caused by neoplastic involvement by lung malignancy .
neoplastic involvement of the phrenic nerve accounts for one third of cases of diaphragmatic paralysis .
other mediastinal tumors that may affect the phrenic nerve include thymomas , lymphomas , and germ cell tumors . in our case , elevated right diaphragm seen on ct along with perihilar lung lesion , gave a clue toward phrenic nerve palsy .
other causes include - lung volume loss ( atelectasis , lobar collapse , partial lung resection , radiation fibrosis , and congenital hypoplasia ) , congenital eventration and abdominal diseases ( dilated stomach or colon , hepatomegaly , splenomegaly , subphrenic abscess ) . in our
case congenital eventration of the diaphragm was another possibility that can give rise to similar scan findings .
however , this was ruled out on the basis of normal report of his chest x - ray performed 4 years ago ( as a part of pre - employment check - up ) . to conclude , we present pet / ct findings in a case of lung carcinoma , where increased fdg uptake was noted in accessory muscles of respiration and unilateral diaphragm . as in our case , this intriguing uptake pattern could be an ancillary finding to contralateral diaphragmatic paralysis .
in known cases of a lung / mediastinal neoplasm , phrenic nerve palsy can be the cause of such a pattern .
 a 36-year - old indian man , a recently diagnosed case of the right lung carcinoma underwent fluorodeoxyglucose positron emission tomography - computed tomography ( fdg pet / ct ) for staging of the malignancy . 
 pet / ct showed increased fdg uptake in the right lung mass , consistent with the known primary tumor . 
 right hemidiaphragm was found to be elevated on ct , suggesting right diaphragmatic paresis . 
 the pet scan demonstrated asymmetric , intense fdg uptake in the left hemidiaphragm and accessory muscles of respiration , which was possibly due to compensatory increased workload related to contralateral right diaphragmatic paresis . 
 the right diaphragmatic paresis was hypothesized to be caused by phrenic nerve palsy by right lung neoplasm . 
INTRODUCTION
CASE REPORT
DISCUSSION