The most common types of peripheral nerve tumors are benign. The two most common types are Schwannomas, which usually occur spontaneously and sporadically but may occur as part of the Schwanommatosis Genetic Syndrome (mutation on chromosome 17) when several are present, and Neurofibromas which usually present as part of the NF1 genetic syndrome (mutation also on chromostome 17 – one of most common genetic mutations with prevalence of 1 in 3,500). Many of these tumors stop growing for very long periods of time and therefore are asymptomatic and may be observed with serial imaging studies (MRN and/or ultrasound). The symptomatic tumors usually present with pain, numbness, and/or weakness. Symptomatic and/or growing tumors should be considered for biopsy and surgical resection. Many of these tumors are can be surgically removed with minimal damage to functioning nerve fibers resulting in minimal or no loss of function. Sometimes, especially in the case of plexiform neurofibromas, resection is limited due to the intimate association of functioning nerve fibers and tumor tissue. Particularly in the setting of partially resected tumors, a postoperative MRN study with contrast should be performed which can serve as a baseline going forward. If malignancy is suspected a specialized team dealing with such challenging tumors should be consulted: further diagnostic studies often include a CT of the chest and abdomen as well as a bone scan looking for evidence of metastatic spread, a PET CT study and/or MRN with diffusion study to look for evidence of malignancy, and an open or percutaneous biopsy is often performed to confirm the diagnosis. A surgical resection combined with additional treatment such as radiotherapy is usually recommended if the tumor proves to be malignant. Again, malignant peripheral nerve tumors should be managed by a team of specialists who frequently deal with such challenging cancer problems.
- Kliot, Y. Ince, T. Tihan. M. Wilson, and M. Kliot. To grow or not to grow, that is the question. Thinking Outside The Box Section of New Developments On The Horizon Supplement. Surg Neurol Int; 4:S407-10. 2013.
- Kwok, J. Slimp, D. Born, R. Goodkin, and M. Kliot. The evaluation and management of benign peripheral nerve tumors and masses. M.S. Berger and M.D. Prados (ed.s). In: Textbook of Neuro-Oncology. Philadelphia, W.B. Saunders. 2004. pp 535-563 (Chapter 73).
E.L. Yuh, S.K. Jain, G.M Lagemann, M. Kliot, P.R. Weinstein, N.M Barbaro, and C.T. Chin. Diffusivity measurements from MR neurography differentiate benign from malignant lesions in patients presenting with peripheral neuropathy. AJNR 36: 203-209. 2015.
The diagnosisandtreatmentof peripheral nerve entrapment syndromes (eg
Carpal Tunnel Syndrome, Ulnar Nerve Compression Across the Elbow, to mention only a few) depends on an understanding of their different clinical grades that reflect severity of nerve damage and the resulting symptoms.
A mildclinical grade occurs with intermittent symptoms but no evidence of axonal loss as shown on clinical exam by muscle atrophy (loss or wasting) on motor examination and/or increased 2 point discrimination (the ability to detect two small points applied to the skin, usually on the finger tips, several millimeters apart) on sensory examination and no evidence of muscle denervation on EMG (electromyographic) testing. A moderateclinical grade occurs with constant symptoms but no clinical or EMG evidence of axonal loss. A severeclinical grade occurs with clinical and EMG evidence of axonal loss.
A mild clinical grade entrapment syndrome is initially treated with non-surgical measures (eg splinting, ergonomic modifications, and physical/hand therapy) while in the case of a severe clinical grade entrapment syndrome surgical decompression is usually recommended. A moderate clinical grade entrapment syndrome can be treated either surgically or non-surgically: if non-surgical therapy fails then surgery is recommended.
G.A. Grant, R. Goodkin, and M. Kliot. Evaluation and surgical management of peripheral nerve problems. Neurosurgery 44: 825-840. 1999.
“Regression to the mean” is a very important concept with significant clinical implications. Most chronic diseases have a fluctuating clinical course. For example, patients with chronic back pain will have pain that varies from day to day and can be exacerbated by certain postures and/or activities. Patients will usually contact a physician when their symptoms are most severe. Therefore if nothing were to be done, it is likely but not certain,that the symptoms would improve over time as the severity reduces or regresses to its mean (average) level. It is therefore not uncommon for patients’ symptoms to improve by the time they see their physician. This does not mean that no intervention should be done. However it does make it difficult to determine what if any effect an intervention is actually having on a clinical outcome. Regression to the mean, as well as the powerful placebo effect (the topic of another future blog), are factors that can exert significant effects that are difficult to control for. One way to do so is to design rigorous clinical double blind randomized controlled trials that subject groups of patients that are statistically similar to protocols that differ in a specific manner without the patients or evaluators being aware of this treatment difference. By doing so, any difference in outcome can be attributed to the treatment given since the effect of other factors should average out. Regression to the mean is a very important concept to keep in mind when evaluating and treating patients with chronic diseases whose clinical manifestations fluctuate significantly over time.
A.G. Barnett, J.C. van der Pols, and A.J. Dobson. Regression to the mean: what it is and how to deal with it. The International Journal of Epidemiology: 34: 215-220. 2004.
- Ariely. Predictably Irrational, Revised and Expanded Version: The Hidden Froces That Shape Our Decisions. Harper Collins. 2009.