Biases may be difficult to control, no concurrent control arm for comparison.
It would be difficult to ascribe the concurrent presence of pain allodynia and paresthesias (which characterizes FM) to a pathogenesis different from an intrinsic nervous system alteration.
However, the presence of concurrent in situ or invasive carcinoma can be difficult to diagnose.
In conventional DSC, it is difficult to prevent the concurrent occurrence of the exothermic reactions of PAN with melting.
Moreover, signal transduction networks operate over a wide range of time-scales, and due to the presence of feedback loops and cross talk it is difficult to discern how concurrent signals are processed.
Some authors have also used topical amphotericin B irrigations into the postoperative sinonasal cavity, although optimal dosing is unknown and efficacy is difficult to determine distinct from other concurrent therapies.
The reason may be that the effects of bottle-feeding on occlusion were difficult to assess when bottle-feeding was concurrent with breast-feeding.
Whether decreased vision was a direct result of the SRD is difficult to ascertain due to high prevalence of concurrent intraretinal macular edema, which may also cause reduced visual acuity.
Even though the results of all the concurrent chemoradiotherapy trials are difficult to compare due to differences regarding dose, timing of intra-arterial infusion and duration of follow-up [ 5- 7, 23, 24], our study confirmed that the percentage of post-treatment complete response is very high (96%) (table 6) and superior to induction intra-arterial chemotherapy protocols [ 15, 25, 26].
Other potential limitations that are difficult to anticipate but will be documented are concurrent health initiatives that may begin in a community during the effectiveness study.
Our study failed to show an advantage with the use of aggressive combination chemotherapy with concurrent radiotherapy although it is difficult to conclude firmly on this because the accrual target was not reached.
