P38 Clinical pearl: pharmaceutical management of primary erythromelalgia (pe) (scn9a)

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Abstract

Situation

Patient RL is a 7 year old female with a confirmed genetic diagnosis for Primary Erythromelalgia PE, with a heterozygous sequence change in the SCN9A gene: c.2623C>G, p.(Gln875Glu). This genetic mutation of SCN9A results in sodium chanellopathy specifically for the voltage gated sodium channel Nav1.7. This genetic mutation makes the Nav1.7 channel hypersensitive to stimulus and over activation.1 As a result, she suffers from severe intermittent episodes of bilateral erythema and burning pain of the lower limbs. These symptoms are difficult to manage and PE is also known as ‘man-on-fire syndrome’.1

Background

PE in a child is a complex diagnosis with severely limited pharmacological treatments available. Inadequate pain relief was achieved with routine analgesics such as paracetamol and ibuprofen. A multidisciplinary team (MDT) approach including pharmacy was implemented with; review of available literature, alternative medications for relief of pain and other PE symptoms, advice on formulation and dosing.

Outcome

When initially diagnosed, RL was frequently admitted to hospital for uncontrollable and pain and the family were unable to manage at home. Since her diagnosis and full MDT involvement, her pain relief has improved, her hospital admissions have decreased and her family are coping better at home. However, despite pharmacological interventions she is still not entirely free from pain and her other symptoms. Patient RL has also received intensive psychology input for coping strategies in managing her pain, and her parents have received psychological and social input to help them. She is managing to walk more and but still relies on her pushchair. Her current medication regimen is as follows: gabapentin, cetirizine, chlorphenamine, naproxen, paracetamol, clonidine, mexiletine, amitriptyline and topical application of amitriptyline and ketamine. Unsuccessful treatments included: magnesium supplementation, menthol in aqueous cream, lidocaine patches, tramadol and aspirin.

Lessons learnt

There is little information in the literature on the treatment of paediatric patients with PE and they are mainly case reports. Management of RL has been multidisciplinary with pharmacy playing an important role advising on treatment of anecdotal evidence, dosing and formulation advice, counselling, sourcing amitriptyline and ketamine gel and therapeutic drug monitoring for mexiletine. Future treatments we hope to trial include novel drugs still in development that specifically target the voltage gated sodium channel Nav1.7 such as raxatrigine.

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