Thursday, March 26, 2015

Diagnosis of PLP is not as obvious as one would think

Diagnosis of PLP seems obvious, right? Somebody feels agonizing pain in their lost limb, and of course we know what it is. Well, sometimes, but other conditions must be ruled out to ensure the treatment fits the problem.


Conditions to Rule Out

Psychogenic limb pain--very rare and impacted by emotional and mental problems of the patient. It occurs when "the patient misinterprets [sic] nonpainful phantom sensations" (Jain, 2011).

Residual Limb Pain (RLP)--Although it triggers phantom pain, it is localized in the stump and not associated with central mechanisms. A differentiation method showing that PLP is diminished only by IV morphine but RLP is diminished by both IV morphine and lidocaine is supported by "A randomized, double-blind, active placebo controlled, crossover trial" (Jain, 2011).

Lesions of the brachial plexus and spinal nerve roots--If amputees have been pain free in the past, this is a potential hypothesis related to local nerve damage unrelated to amputation and occurring at a later date.

Lesions of the central nervous system--stroke or spinal cord injury can cause neuropathic pain in the phantom limb, yet the quality of pain may help differentiate.

Phantom Sensations (PS)--this may not be possible to differentiate because the some of the same mechanisms as PLP are implicated. Furthermore, patients are frequently unable to distinguish between the two, such as when a contorted phantom limb sensation causes pain.


Diagnostic Workup

The optimal diagnostic workup for PLP includes a thorough evaluation preceding amputation, including pain and psychological assessments. Following amputation, a pain assessment and neurological examination should be performed. Tinel sign and and MRI can detect the presence of a neuroma, which is hypothesized to be one component of PLP (and also RLP), so that could contribute to confusion.


No online videos of Tinel Sign in amputees, but this gives you an idea.
https://www.youtube.com/watch?v=RV2Ic7sY9M4


Sources:


Jain, K. (2011). Phantom Limb Pain Diagnostic Workup. In MedMerits Free access to information doctors rely on. Retrieved March 26, 2015, from http://www.medmerits.com/index.php/article/phantom_limb_pain/P8

Jain, K. (2011). Phantom Limb Pain Differential Diagnosis. In MedMerits Free access to information doctors rely on. Retrieved March 26, 2015, from http://www.medmerits.com/index.php/article/phantom_limb_pain/P7

Clarke, C., Lindsay, D. R., Pyati, S., & Buchheit, T. (2013, June). Residual Limb Pain is Not a Diagnosis A proposed Algorithm to Classify Postamputation Pain. Clin J Pain, 29(6), 551-562.

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