Your description of the shoulder pain suggests that the pain is not a sign of intrinsic disease of the shoulder itself, but rather it is called referred pain, such pain most commonly associated with disease of the gall bladder. Referred shoulder pain has been reported to occur not just with direct irritation of the phrenic nerve, but with disease under the diaphragm within the abdomen called sub-diaphragmatic, with traumatic liver and biliary tract injury, sub-diaphragmatic endometriosis, adrenal hematoma, cholecystitis, intestinal rupture/leakage, including the stomach and pancreatitis. Speculation is that the pain is related to diaphragmatic irritation and that impulses from mechanical or chemical stimulation/irritation are carried to the brain via the phrenic nerve. It has also been suggested that impulses along these same (afferent) phrenic nerve fibers can modulate respiratory rate and induce the perception of dyspnea, commonly called shortness of breath. In this regard, it might be more likely that the problem breathing while lying down, also known as orthopnea, would be related to impairment of the phrenic nerve motor fibers to the diaphragm and this would be consistent with the “degradation” demonstrated by the SNIFF test and the worsened phrenic nerve conduction tests.
Bottom line, something is compressing or otherwise effecting your phrenic nerve, perhaps inflammation. If compression is the cause, the site and cause might be revealed by CT scanning, magnetic resonance imaging (MRI) and/or positron emission tomography (PET) scanning.
Recurrent disease beneath the diaphragm could account for the referred pain but probably not for the deterioration of the phrenic motor nerve fibers.
You might want to discuss the above with your doctors. Please give us a follow-up on your condition.
Thank you for your quick reply. Current issues: CT scan 3 weeks ago and PET scan 1 week ago show several areas of concern within abdomen, chest, and pelvis, although none are particularly large on CT or have more than "mild" uptake in PET. Oncologist and pulmonologist feels none of them are where they could be directly impinging on R. phrenic nerve. Needle biopsy scheduled for next week. Question - could my heavy duty (31 treatments) radiation treatment 4 years ago after my surgery (primarily in area of L. upper lobe) caused damage to the R. phrenic nerve, that only showed up after 4 years ??