Neuro-Ophthalmologic Manifestations of Myoclonic Epilepsy with Ragged Red Fibers (MERRF)

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Article initiated by:

Andrew Go Lee, MD, Peter W. Mortensen, MD, Rachel A Stroh, Subahari Raviskanthan, MBBS

All contributors:

Nagham Al-Zubidi, MD, Subahari Raviskanthan, MBBS

Assigned editor:

Sonali Singh MD

Review:

Assigned status Update Pending

 by Sonali Singh MD on April 14, 2021.

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Contributing Editors:	add

Disease Entity

Myoclonic Epilepsy with Ragged Red Fibers (MERRF) is recognized by the following International Center for Diseases (ICD) codes:

ICD-10: E88.4

Disease

Myoclonic Epilepsy with Ragged Red Fibers (MERRF) is a mitochondrial disorder associated with a mitochondrial gene mutation for the gene encoding the tRNA for lysine. This mutation is usually an A to G point mutation at np 8344. MERRF usually presents in early childhood with myoclonic epileptic (ME) episodes and the muscle biopsy confirms the ragged red fibers (RRF). It can later progress to include other neurological features, including cerebellar ataxia, sensorineural hearing loss, peripheral neuropathy, mental retardation, dementia, optic atrophy, and myopathy with ragged red fibers on biopsy due to lactic acidosis and mitochondrial proliferation.  

Ophthalmological Manifestations

Ophthalmological manifestations include optic neuropathy, ophthalmoplegia, , pigmentary retinopathy , ptosis , low visual acuity, and nystagmus.

Author	Title	N	Ophthalmological Manifestations
Cheng-Cheng Zhu et al.	Ophthalmological findings in 74 patients with mitochondrial disease	2	2/2 Decreased extraocular movement
Raymond P. Najjar et al.	Retinal Neuronal Loss in Visually Asymptomatic Patients With Myoclonic Epilepsy With Ragged-Red Fibers	3	3/3 visually asymptomatic 3/3 had thinning of retinal nerve fiber layers and macular ganglion cell complexes
M A Grönlund et al.	Ophthalmological findings in children and young adults with genetically verified mitochondrial disease	7	1/7 ptosis 3/7 reduced eye motility 1/7 nystagmus 2/7 low visual acuity 6/7 optic nerve atrophy 1/7 retinal dystrophy
Mancuso, Michelangelo MD et al.	Phenotypic heterogeneity of the 8344A>G mtDNA "MERRF" mutation	34	10/34 ptosis 2/34 ophthalmoparesis
Mancuso, Michelangelo MD et al.	Myoclonus in mitochondrial disorders	24	2/24 optic neuropathy 4/24 retinopathy 6/24 ptosis/ophthalmoparesis

Prevalence

Mitochondrial disorders are relatively uncommon but  may have a prevalence of up to 1 in 5000. The epidemiological data for MERRF is largely unknown, but the prevalence is estimated to be around 1 in 100,000 or less.

In summary, MERRF is a mitochondrial disorder characterized by myoclonic epilepsy and ragged red fibers on muscle biopsy. The neuro-ophthalmic findings include optic atrophy, ophthalmoplegia, ptosis, or pigmentary retinopathy. There is no cure, but supportive measures are recommended.

Diagnosis

MERRF has four clinical features that can be used in diagnosis: myoclonus, generalized epilepsy, ataxia, and ragged-red fibers in a muscle biopsy. Molecular genetic testing can also be used to confirm the diagnosis, with most patients having the 8344 A>G point mutation (present in 80% of MERRF patients).

Management

Treatment

As with treatment of many mitochondrial disorders, drugs like ubiquinol, carnitine, alpha lipoic acid, vitamin E, vitamin B complex, or creatine can be considered. These drugs do not provide benefit in all patient populations and can be discontinued if they are ineffective. Seizures can be treated with any traditional anticonvulsant except valproic acid, due to its interaction with mitochondrial respiration. MERRF myoclonus is usually treated with levetiracetam or clonazepam. Any impaired motor ability can be improved with physical therapy or aerobic exercise.