Overview
Monomelic amyotrophy (MMA) is a rare neurological condition that causes muscle wasting and weakness in one arm or, less commonly, one leg. The name comes from Greek words meaning 'single limb' and 'muscle wasting.' It is also known as Hirayama disease (when it affects the arm), benign focal amyotrophy, or juvenile muscular atrophy of the distal upper extremity. The condition mainly affects the muscles controlled by the lower part of the spinal cord in the neck region, leading to shrinking and weakening of the hand and forearm muscles on one side of the body. MMA most often starts in young men during their teens or early twenties. The weakness usually gets worse slowly over a few years and then stops progressing on its own — this is one of the features that makes it different from more severe motor neuron diseases. The exact cause is not fully understood, but one leading theory suggests that repeated forward bending of the neck compresses the spinal cord over time, cutting off blood supply and damaging nerve cells. There is no cure for MMA, but the good news is that the disease usually stabilizes on its own. Treatment focuses on managing symptoms, preventing further damage (sometimes with a neck collar to limit bending), and physical therapy to maintain strength and function. Most people with MMA can live normal lifespans and maintain a good quality of life, though some permanent weakness in the affected limb is common.
Also known as:
Key symptoms:
Weakness in one hand or forearmMuscle wasting (shrinking) in one hand or forearmDifficulty gripping objects or performing fine hand movementsTrembling or shaking of the fingers when the arms are outstretchedCold hands or fingers on the affected sideWeakness that gets worse temporarily in cold weatherAsymmetric appearance of the hands or arms (one looks thinner than the other)Occasional mild cramping in the affected hand or armWeakness that slowly worsens over a few years then stabilizes
Clinical phenotype terms (10)— hover any for plain English
Sporadic
Usually appears on its own, not inherited from a parent
Juvenile
Begins in the teen years
FDA & Trial Timeline
1 eventAll India Institute of Medical Sciences — NA
Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.
Treatments
No FDA-approved treatments are currently listed for Monomelic amyotrophy.
1 clinical trialare actively recruiting — trials can provide access to cutting-edge therapies.
View clinical trials →Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Monomelic amyotrophy.
Community
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Start the conversation →Latest news about Monomelic amyotrophy
Disease timeline:
New recruiting trial: Cervical Fixation Surgery Cervical Collar for Management of Hirayama Disease: A Randomized Study
A new clinical trial is recruiting patients for Monomelic amyotrophy
Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.Is my diagnosis confirmed, and what tests were used to rule out other conditions?,Should I be wearing a cervical collar, and if so, how often and for how long?,How quickly do you expect my symptoms to progress, and when might they stabilize?,Are there any activities or movements I should avoid to protect my spine?,What physical or occupational therapy do you recommend, and how often should I attend?,Are there any clinical trials or new treatments I should know about?,How often should I have follow-up appointments and repeat imaging?
Common questions about Monomelic amyotrophy
What is Monomelic amyotrophy?
Monomelic amyotrophy (MMA) is a rare neurological condition that causes muscle wasting and weakness in one arm or, less commonly, one leg. The name comes from Greek words meaning 'single limb' and 'muscle wasting.' It is also known as Hirayama disease (when it affects the arm), benign focal amyotrophy, or juvenile muscular atrophy of the distal upper extremity. The condition mainly affects the muscles controlled by the lower part of the spinal cord in the neck region, leading to shrinking and weakening of the hand and forearm muscles on one side of the body. MMA most often starts in young men
How is Monomelic amyotrophy inherited?
Monomelic amyotrophy follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Monomelic amyotrophy typically begin?
Typical onset of Monomelic amyotrophy is juvenile. Age of onset can vary across affected individuals.
Are there clinical trials for Monomelic amyotrophy?
Yes — 1 recruiting clinical trial is currently listed for Monomelic amyotrophy on UniteRare. See the clinical trials section on this page for phase, sponsor, and site details sourced from ClinicalTrials.gov.
Which specialists treat Monomelic amyotrophy?
3 specialists and care centers treating Monomelic amyotrophy are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.