Working Diagnosis:
Hereditary neuropathy with liability to pressure palsies (HNPP) with foot drop secondary to MCL brace compression of the peroneal nerve.

Treatment:
Genetics offered her a comprehensive neuropathies genetic testing panel, however, she declined at the time out of reasonable concern for future insurance consequences. Instead, she opted for conservative therapy with the presumptive diagnosis of HNPP. CMT was also considered, but her (and her father's) athleticism and sporting activity without difficulty argued against it.

Outcome:
At 3 month follow up, her knee instability and foot drop improved. Emphasis was placed on strategies to prevent future nerve compression. She had returned to running but not yet to soccer. This case illustrates how even typically benign therapies can have unexpected side effects and serves as a reminder to consider underlying genetic predispositions in patients presenting with neuropathy.

Author's Comments:
HNPP is typically characterized by repeated focal pressure neuropathies, often presenting in the 2nd decade of life. Some are left with mild residual disability, although most recover completely. Workup should be initiated in an adult with recurrent focal compression neuropathies and has a family history of similar episodes consistent with autosomal dominant inheritance. The only known associated gene is PMP22, which mainly occurs as a deletion of chromosome 17p11.2. Genetic testing allows diagnosis although often does not change management, and instead allows employment of prevention strategies, as treatment is primarily supportive. Surgical risks often outweigh benefits.

Editor's Comments:
This clinical case highlights a classic case of HNPP with a known family and person history of recurrent sensory and motor symptoms in single or multiple nerves. Fortunately, a vast majority of patients have mild to no resulting disability.

Diagnosis may be difficult as symptoms can come and go, but electrophysiology studies, ultrasound and MRI imaging may help solidify a diagnosis, if genetic testing is not readily available. Electromyography and nerve conduction studies often show prolongation of distal nerve conduction latencies, especially of the median nerve at the wrist and the common peroneal nerve at the level of the fibular head. Ultrasound and MRI may show multi-focal increase in nerve cross-sectional area, especially at or near entrapment sites.

Once the diagnosis is made, treatment is symptomatic and can include occupational and physical therapy to address issues with fine motor and gross motor skills, transient bracing, and the use of protective pads at elbows and knees to prevent pressure and trauma to the local nerves.

In terms of prevention, it is recommended that patients avoid prolonged sitting with legs crossed, repetitive wrist and elbow movements, or any prolonged leaning or rest on their elbows. In the case of our patient who notes frequent paresthesias to her arms and legs when sleeping, adding a foam mattress topper or sleeping with ankle/wrist supports may help lessen pressure on affected nerves.

References:
Attarian S, Fatehi F, Rajabally YA, Pareyson D. Hereditary neuropathy with liability to pressure palsies. J Neurol. 2020 Aug;267(8):2198-2206. doi: 10.1007/s00415-019-09319-8. Epub 2019 Apr 15. PMID: 30989370.
Chrestian N. Hereditary Neuropathy with Liability to Pressure Palsies. 1998 Sep 28 [updated 2020 Aug 27]. In: Adam MP, Everman DB, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2022. PMID: 20301566.

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