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Health condition

Diffuse midline glioma, H3 K27-altered - a rare, aggressive brain tumour.

The umbrella that includes DIPG. A specialist paediatric neuro-oncology team, early trial conversations and compassionate supportive care matter from the first scan.

A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Aligned with WHO 2021 CNS tumour classification, NICE guidance and specialist paediatric neuro-oncology consensus.

  • 03

    Current for 2026

    Reflects the H3 K27-altered designation, emerging trials such as ONC201 and current UK specialist commissioning.

Key facts

DMG at a glance.

The essentials, in plain English - what it is, where it grows, what defines it and how it is treated in the UK today.

  • What it is

    Diffuse midline glioma, H3 K27-altered - a rare, aggressive WHO grade 4 glioma of the brainstem, thalamus, spinal cord or cerebellum.

  • DIPG

    Diffuse intrinsic pontine glioma - the pontine subtype - is the classic paediatric presentation with a devastating course.

  • Who it affects

    Peak incidence age 4 to 11 with median diagnosis 6 to 9 years - occurs in adults too and affects boys and girls equally.

  • Molecular hallmark

    H3 K27M mutation in H3F3A or HIST1H3B, or EZHIP overexpression - defining alterations under WHO 2021.

  • Mainstay treatment

    Fractionated radiotherapy - typically around 54 Gy over 6 weeks - offers transient symptomatic benefit but is not curative.

  • Prognosis

    Median survival for paediatric DIPG remains 9 to 12 months despite treatment - trials such as ONC201 are the current hope.

Why this guide matters

Specialist care, from the first scan.

A rare and devastating diagnosis - but one where specialist paediatric neuro-oncology teams, molecular testing and trial access change the conversation.

  • Specialist MDT from day one

    Care should be led by a commissioned paediatric neuro-oncology centre with experience of DMG and its molecular workup.

  • Molecular typing matters

    H3 K27M immunohistochemistry, molecular testing and increasingly CSF liquid biopsy define diagnosis and trial eligibility.

  • Trials are the current hope

    Agents such as ONC201 (dordaviprone) offer the first meaningful advances in decades - ask about CONNECT, BIOMEDE and PNOC.

How the diagnosis is made

From first symptoms to a specialist plan.

The steps a UK team will normally follow - urgent imaging first, then molecular testing and MDT-led planning at a specialist paediatric centre.

  1. 01

    Assessing

    History and neurological exam

    Rapid days-to-weeks onset of cranial nerve palsies, long tract signs and cerebellar features prompts urgent imaging.

  2. 02

    Assessing

    Fundoscopy and cranial nerves

    Papilloedema, sixth and seventh nerve palsies, dysarthria, dysphagia and facial droop are classic for pontine disease.

  3. 03

    Assessing

    Urgent MRI brain and spine

    Gadolinium-enhanced MRI shows an expansile T2/FLAIR hyperintense pontine mass that engulfs the basilar artery in DIPG.

  4. 04

    Confirming

    MR spectroscopy and perfusion

    Advanced sequences help characterise the lesion and rule out mimics such as low-grade glioma or ependymoma.

  5. 05

    Confirming

    Stereotactic biopsy

    Historically avoided in DIPG - now increasingly performed at specialist centres for molecular typing and trial access.

  6. 06

    Planning

    H3 K27M testing and CSF ctDNA

    Immunohistochemistry and molecular testing confirm the diagnosis. CSF liquid biopsy for H3K27M is an emerging option.

  7. 07

    Planning

    Specialist paediatric MDT

    Care is coordinated through commissioned centres such as Great Ormond Street, Birmingham, Alder Hey, Bristol and the Royal Marsden.

Typical timeline: urgent scan within days, MDT-led plan within one to two weeks.

Symptoms

What DMG looks like clinically.

The classic pontine triad, plus thalamic and spinal presentations - and the features that mean same-day imaging is needed.

  • Cranial nerve palsies

    Sixth and seventh nerve palsies, dysarthria, dysphagia and facial droop are the classic pontine features.

  • Long tract signs

    Limb weakness, hyperreflexia and an upgoing plantar reflex point to corticospinal involvement.

  • Cerebellar features

    Ataxia, dysmetria and gait unsteadiness reflect cerebellar peduncle and pathway disruption.

  • Raised intracranial pressure

    Headache, morning vomiting, diplopia and behaviour change can herald hydrocephalus.

  • Thalamic presentation

    Hemiparesis, sensory loss, cognitive change and hydrocephalus can dominate thalamic DMG.

  • Spinal cord presentation

    Back pain, weakness, a sensory level and bladder or bowel disturbance suggest a spinal midline lesion.

  • Adult presentations

    Adults with H3 K27-altered gliomas often have a longer, more indolent course than paediatric DIPG.

  • Red flag - rapid deterioration

    Any rapidly evolving cranial nerve, motor or cerebellar picture in a child needs same-day neuroimaging.

Treatment

How DMG is treated in the UK.

Radiotherapy is the mainstay. Molecular typing opens the door to trials such as ONC201. Supportive and palliative care run alongside from the start.

  • Fractionated radiotherapy

    Around 54 Gy over 6 weeks - the mainstay of care. Offers transient symptomatic relief and a few months of survival benefit.

  • Proton beam therapy

    Selected patients may be considered - reduces dose to surrounding brain in eligible thalamic or spinal cases.

  • Stereotactic biopsy

    Not a treatment but increasingly performed at specialist centres for molecular characterisation and trial eligibility.

  • Partial resection

    Occasionally feasible for thalamic or spinal DMG in expert hands - not appropriate for pontine DIPG.

  • ONC201 (dordaviprone)

    A dopamine receptor D2 antagonist and ClpP agonist showing meaningful activity in H3 K27M-mutant disease within trials.

  • Targeted trial agents

    Paxalisib (GDC-0084, PI3K/mTOR), panobinostat (HDAC inhibitor) and imipridones are being evaluated in national and international trials.

  • Cellular and immune therapy

    CAR-T approaches targeting GD2, B7-H3 and EGFR, peptide vaccines and oncolytic virus platforms are in early-phase trials.

  • Supportive and palliative care

    Dexamethasone, anticonvulsants, PEG feeding, physiotherapy, SLT and specialist paediatric palliative care are central throughout.

What this guide is based on

The sources behind every claim on this page.

UK national guidance, WHO classification and specialist paediatric neuro-oncology consensus, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your specialist paediatric neuro-oncology team knows the child and family and can tell you which parts of this guide apply. If in doubt, ask.

  • WHO Classification of Tumours of the Central Nervous System (5th ed., 2021) - diffuse midline glioma, H3 K27-altered.

  • NICE. Brain tumours (primary) and brain metastases in adults (NG99) and referral for suspected cancer (NG12).

  • Children's Cancer and Leukaemia Group (CCLG) and specialist paediatric neuro-oncology consensus documents.

  • The Brain Tumour Charity, Abbie's Army and DIPG Advocacy Group - patient information and research updates.

Red flags

When to seek urgent help.

Symptoms that should trigger a same-day paediatric review or a return to the specialist team.

  • New squint or double vision in a child

    Sudden strabismus, sixth nerve palsy or diplopia deserves urgent same-day paediatric assessment and imaging.

  • Facial droop or swallowing change

    New facial weakness, dysarthria or choking on feeds points to brainstem pathology until proven otherwise.

  • Morning headache and vomiting

    Persistent early-morning headache with vomiting in a child is a red flag for raised intracranial pressure.

  • Rapid neurological deterioration

    Days-to-weeks evolution of weakness, ataxia or cranial nerve signs needs emergency neuroimaging.

  • Behaviour or personality change

    Unexplained change in mood, cognition or school performance alongside neurological signs warrants review.

  • Back pain with weakness

    Spinal DMG can present with progressive back pain, limb weakness or bladder and bowel disturbance.

  • Hydrocephalus signs

    Bulging fontanelle in infants, sunset eyes, drowsiness or vomiting need immediate neurosurgical review.

  • Steroid weaning symptoms

    Rapid return of neurological symptoms as dexamethasone is tapered should be discussed with the specialist team.

  • Psychological distress

    The impact on the child, siblings and parents is profound - specialist psychological and palliative support should be offered early.

Living with it

A specialist path, walked with support.

Four things that make the biggest difference for families - a coordinated MDT, trial access, charity support and, where families choose, a research legacy.

A quiet reminder

Palliative care is not the last chapter.

Specialist paediatric palliative teams work alongside active treatment from early on, supporting symptoms, dignity and the whole family.

  1. 01 Team

    A specialist team around you

    Care is led by paediatric neuro-oncology MDTs at commissioned UK centres with shared care closer to home where possible.

  2. 02 Trials

    Ask about clinical trials

    National and international trials - CONNECT, BIOMEDE, PNOC and others - are the route to novel agents such as ONC201.

  3. 03 Support

    Lean on the charities

    Abbie's Army, the DIPG Advocacy Group, The Brain Tumour Charity and Children with Cancer offer practical and emotional support.

  4. 04 Legacy

    Research donation and legacy

    Families can consider brain donation for research - a profound contribution that helps future children.

Frequently asked

Everything families ask about DMG.

Clear answers on DIPG, biopsy, radiotherapy, ONC201 and prognosis.

  • What is diffuse midline glioma?

    Diffuse midline glioma (DMG), H3 K27-altered, is a rare and highly aggressive WHO grade 4 glioma that arises in midline structures of the central nervous system - most commonly the brainstem (pons), thalamus, spinal cord or cerebellum. Its defining feature under the WHO 2021 classification is either an H3 K27M mutation (in H3F3A or HIST1H3B) or EZHIP overexpression.

  • Is DIPG the same as diffuse midline glioma?

    DIPG - diffuse intrinsic pontine glioma - is a subtype of diffuse midline glioma affecting the pons. It is the classic paediatric brainstem tumour and the most extensively studied form. Almost all DIPGs carry the H3 K27M alteration, so most sit within the DMG umbrella under the current WHO classification.

  • How is diffuse midline glioma diagnosed?

    Diagnosis begins with a careful history and neurological examination, followed by an urgent MRI of the brain and spine with gadolinium. In pontine DIPG the MRI appearance can be characteristic - an expansile T2/FLAIR hyperintense mass that engulfs the basilar artery. Where safe and clinically useful, a stereotactic biopsy at a specialist paediatric neurosurgical centre allows H3 K27M testing and trial eligibility. CSF liquid biopsy for H3K27M is an emerging tool.

  • Can diffuse midline glioma be operated on?

    For DIPG in the pons, surgical resection is not feasible because of the critical location. Stereotactic biopsy for molecular characterisation is increasingly offered at specialist centres. Thalamic and spinal DMGs can sometimes be partially resected by expert paediatric neurosurgeons, but complete removal is rarely possible.

  • What treatments are available?

    Fractionated external beam radiotherapy - typically around 54 Gy over 6 weeks - is the mainstay and offers transient symptomatic improvement and a modest survival benefit. Traditional chemotherapy has not shown proven benefit. The most promising current avenue is targeted therapy in clinical trials, particularly ONC201 (dordaviprone) for H3 K27M-mutant disease. Supportive care with dexamethasone, anticonvulsants, feeding support, physiotherapy and specialist paediatric palliative care is central throughout.

  • What is the outlook?

    Diffuse midline glioma carries a devastating prognosis. Median survival for paediatric DIPG remains around 9 to 12 months despite treatment, and long-term survival is very rare. Adult H3 K27-altered gliomas often have a somewhat longer course. Trials of agents such as ONC201 and cellular therapies offer the first meaningful advances in decades and give a strong reason to seek specialist care and trial access early.

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