Phenotypic Variability Leads to Under-recognition of HNPP

Anesthetic Considerations for Patients with Hereditary Neuropathy with Liability to Pressure Palsies: A Narrative Review

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant demyelinating neuropathy characterized by an increased susceptibility to peripheral nerve injury from trauma, compression, or shear forces. Patients with this condition are unique, necessitating distinct considerations for anesthesia and surgical teams. This review describes the etiology, prevalence, clinical presentation, and management of HNPP and presents contemporary evidence and recommendations for optimal care for HNPP patients in the perioperative period. While the incidence of HNPP is reported at 7-16:100,000, this figure may be an underestimation due to underdiagnosis, further complicating medicolegal issues. With the subtle nature of symptoms associated with HNPP, patients with this condition may remain unrecognized during the perioperative period, posing significant risks. Several aspects of caring for this population, including anesthetic choices, intraoperative positioning, and monitoring strategy, may deviate from standard practices. As such, a tailored approach to caring for this unique population, coupled with meticulous preoperative planning, is crucial and requires a multidisciplinary approach.

Targeting PI3K/Akt/mTOR signaling in rodent models of PMP22 gene-dosage diseases

Haplo-insufficiency of the gene encoding the myelin protein PMP22 leads to focal myelin overgrowth in the peripheral nervous system and hereditary neuropathy with liability to pressure palsies (HNPP). Conversely, duplication of PMP22 causes Charcot-Marie-Tooth disease type 1A (CMT1A), characterized by hypomyelination of medium to large caliber axons. The molecular mechanisms of abnormal myelin growth regulation by PMP22 have remained obscure. Here, we show in rodent models of HNPP and CMT1A that the PI3K/Akt/mTOR-pathway inhibiting phosphatase PTEN is correlated in abundance with PMP22 in peripheral nerves, without evidence for direct protein interactions. Indeed, treating DRG neuron/Schwann cell co-cultures from HNPP mice with PI3K/Akt/mTOR pathway inhibitors reduced focal hypermyelination. When we treated HNPP mice in vivo with the mTOR inhibitor Rapamycin, motor functions were improved, compound muscle amplitudes were increased and pathological tomacula in sciatic nerves were reduced. In contrast, we found Schwann cell dedifferentiation in CMT1A uncoupled from PI3K/Akt/mTOR, leaving partial PTEN ablation insufficient for disease amelioration. For HNPP, the development of PI3K/Akt/mTOR pathway inhibitors may be considered as the first treatment option for pressure palsies.

Efficacy of Spinal Cord Stimulation Using Differential Target Multiplexed Stimulation for Intractable Pain of Hereditary Neuropathy with Liability to Pressure Palsies: A Case Report

Hereditary neuropathy with liability to pressure palsies is an extremely rare genetic disorder; it is an autosomal dominant disorder with a high incidence of neuropathic and/or musculoskeletal pain. A case of achieving pain relief by spinal cord stimulation using differential target multiplexed stimulation for a 44-year-old female patient with hereditary neuropathy with liability to pressure palsies who was experiencing severe pain in her back, face, and all four limbs is presented. In her early teens, the initial symptoms were numbness and weakness of a limb after movement, which improved spontaneously. Transient pain in her back followed by systemic and persistent muscle weakness and pain developed. Deletion of the gene for peripheral myelin protein 22 was detected by peripheral nerve biopsy. The diagnosis of hereditary neuropathy with liability to pressure palsies was made in her early thirties. A spinal cord stimulation trial was performed because her severe pain continued despite administering many medications. Therefore, two spinal cord stimulation systems were implanted at the C3-5 and Th8-9 levels by two procedures. Pain in her back, arms, and legs decreased from 8 to 1, 5 to 1, and 6 to 2 on the numerical rating scale, respectively. Furthermore, opioid usage was tapered. The pain of hereditary neuropathy with liability to pressure palsies has a complicated pathogenesis and is resistant to pharmacological treatment. Spinal cord stimulation using differential target multiplexed stimulation may be a viable treatment option.

Hereditary neuropathy with liability to pressure palsies (HNPP): Intrafamilial phenotypic variability and early childhood refusal to walk as the presenting symptom

BACKGROUND

Limping and/or refusal to walk is a common complaint in the setting of the pediatric department, with a widely diverse differential diagnosis. An unusual etiology, is that of a hereditary neuropathy. Hereditary neuropathy with liability to pressure palsies (HNPP) is a recurrent, episodic demyelinating neuropathy, most commonly caused by a 17p11.2 chromosomal deletion encompassing the PMP22 gene.

METHODS

We pursued chromosomal microarray analysis (CMA) in multiple affected individuals of a single extended family, manifesting a range of phenotypic features consistent with HNPP.

RESULTS

A 4.5 years-old boy presented for in-patient evaluation due to refusal to walk. Initial investigations including spine MRI and bone scan failed to yield a conclusive diagnosis. Following family history, which implied an autosomal dominant mode of inheritance, CMA was pursued and confirmed a 17p11.2 deletion in the proband consistent with HNPP. Importantly, following this diagnosis, four additional affected family members were demonstrated to harbor the deletion. Their variable phenotypic features, ranging from a prenatal diagnosis of a 6 months-old sibling, to recurrent paresthesias manifesting in the fourth decade of life, are discussed.

CONCLUSIONS

Our experience with the family reported herein demonstrates how a thorough anamnesis can lead to a rare genetic etiology with a favorable prognosis and prevent unnecessary investigations, and underscores HNPP as an uncommon diagnostic possibility in the limping child.

Spinobulbar muscular atrophy combined with atypical hereditary neuropathy with liability to pressure palsy

Spinobulbar muscular atrophy (SBMA) is an X-linked recessive disease, presenting motor weakness and wasting of facial, bulbar and limb muscles. Hereditary neuropathy with liability to pressure palsy (HNPP) is autosomal dominant disorder characterized by recurrent neuropathies at common entrapment sites. We report a case of co-existence of SBMA and atypical HNPP with genetic confirmation of CAG expansion in the androgen receptor (AR) gene and deletion of the peripheral myelin protein 22 (PMP22) gene. A 62-year-old man presented with progressive muscle weakness, fasciculations in upper and lower limbs and dysesthesia predominantly in the distal regions. No family members, including his children, experienced similar symptoms. The electrodiagnostic examination was compatible with demyelinating sensorimotor polyneuropathy. Simultaneous hereditary polyneuropathy and motor neuron disease were suspected and relevant genetic testing was confirmed HNPP and SBMA. This case presented with 2 rare genetic neuromuscular disorders and the atypical HNPP phenotype. This case highlight the importance of detailed patient histories, as well as neurological and electrophysiological examinations for diagnosis of atypical and combination of rare genetic disorders.

Hereditary neuropathy with liability to pressure palsies in childhood: Case series and literature update

Hereditary Neuropathy with Liability to Pressure Palsy (HNPP) is a rare condition in childhood with a diverse range of clinical presentations. We analyzed the clinical presentation and electrophysiological data of 12 children with a confirmed PMP22 gene deletion and reviewed the published reports of HNPP in children and compared our data with the reports from the literature review. Peroneal palsy was the most common presentation (42%) followed by brachial plexus palsy in 25% of our cases. Nerve conduction studies were always suggestive of the diagnosis demonstrating 3 major patterns: multifocal demyelination at the area of entrapment, generalized sensory-motor polyneuropathy and a combination of the two first patterns in a vast majority (60%). Surprisingly, there was bilateral or unilateral electrophysiological entrapment of the median nerve at the carpal tunnel in all our patients. The clinical presentation of HNPP in childhood is heterogeneous and electrophysiological findings are helpful in establishing the diagnosis. Any unexplained mononeuropathy or multifocal neuropathy should lead to PMP22 gene testing to look for the deletion. Early diagnosis is important in order to facilitate appropriate genetic counseling and also for the appropriate care for these patients.

Murine therapeutic models for Charcot-Marie-Tooth (CMT) disease

INTRODUCTION OR BACKGROUND

Charcot-Marie-Tooth (CMT) disease represents a broad group of inherited motor and sensory neuropathies which can originate from various genetic aberrations, e.g. mutations, deletions and duplications.

SOURCES OF DATA

We performed a literature review on murine animal models of CMT disease with regard to experimental therapeutic approaches. Hereby, we focussed on the demyelinating subforms of CMT (CMT1). PubMed items were CMT, animal model, demyelination and therapy.

AREAS OF AGREEMENT

Patients affected by CMT suffer from slowly progressive, distally pronounced muscle atrophy caused by an axonal loss. The disease severity is highly variable and impairments may result in wheelchair boundness. No therapy is available yet.

AREAS OF CONTROVERSY

Numerous rodent models for the various CMT subtypes are available today. The selection of the correct animal model for the specific CMT subtype provides an important prerequisite for the successful translation of experimental findings in patients.

GROWING POINTS

Despite more than 20 years of remarkable progress in CMT research, the disease is still left untreatable. There is a growing number of experimental therapeutic strategies that may be translated into future clinical trials in patients with CMT.

AREAS TIMELY FOR DEVELOPING RESEARCH

The slow disease progression and insensitive outcome measures hamper clinical therapy trials in CMT. Biomarkers may provide powerful tools to monitor therapeutic efficacy. Recently, we have shown that transcriptional profiling can be utilized to assess and predict the disease severity in a transgenic rat model and in affected humans.

Hereditary neuropathy with liability to pressure palsies and anaesthesia: peri-operative nerve injury

A 43-year-old female with carcinoma of the left breast underwent wide local excision of the tumour and sentinel lymph node biopsy under general anaesthesia. Three lymph nodes were removed uneventfully during the operation. Postoperatively, the patient complained of weakness and decreased sensation of her left arm. A diagnosis of peri-operative neuropraxia was made. This resolved completely over the following 4 weeks. Genetic testing confirmed a diagnosis of hereditary neuropathy with liability to pressure palsies.