Overview
Focal myositis is a rare inflammatory condition that affects a single muscle or a small group of muscles in one part of the body. Unlike other forms of myositis that affect muscles throughout the body, focal myositis stays localized — meaning it tends to stay in one spot. The condition causes a painful, firm swelling or lump in the affected muscle, most often in the leg, though it can occur in the arm, neck, or other areas. The exact cause is not fully understood, but it is thought to involve the immune system mistakenly attacking muscle tissue in a limited area. The main symptoms include a noticeable lump or swelling in a muscle, local pain or tenderness, and sometimes mild weakness in the affected area. The swelling can appear suddenly and may be mistaken for a tumor, which is why proper diagnosis — usually through imaging and a muscle biopsy — is so important. Focal myositis is also sometimes called localized myositis or pseudotumor of muscle because the swelling can look like a tumor on scans. Most people with focal myositis do well with treatment or even without it, as the condition sometimes resolves on its own. When treatment is needed, anti-inflammatory medications such as corticosteroids are commonly used. The overall outlook is generally favorable, though some people may experience recurrence.
Key symptoms:
A firm, painful lump or swelling in one muscleLocalized muscle pain or tendernessMild weakness in the affected muscleSwelling that appears suddenly or grows over weeksThe affected area may feel warm to the touchLimited range of motion near the swollen muscleFatigue in the affected limb during activity
Clinical phenotype terms (7)— hover any for plain English
Sporadic
Usually appears on its own, not inherited from a parent
Adult
Begins in adulthood (age 18 or older)
Treatments
No FDA-approved treatments are currently listed for Focal myositis.
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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 Focal myositis.
Community
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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 a biopsy needed to confirm my diagnosis, or can imaging alone be enough?,Should I start corticosteroids, or is it safe to watch and wait first?,How will we know if the treatment is working?,What are the chances this condition will come back after it resolves?,Are there any activities I should avoid while the muscle is inflamed?,Should I see a physical therapist to help with strength and recovery?,Are there any signs I should watch for that would mean I need to come back urgently?
Common questions about Focal myositis
What is Focal myositis?
Focal myositis is a rare inflammatory condition that affects a single muscle or a small group of muscles in one part of the body. Unlike other forms of myositis that affect muscles throughout the body, focal myositis stays localized — meaning it tends to stay in one spot. The condition causes a painful, firm swelling or lump in the affected muscle, most often in the leg, though it can occur in the arm, neck, or other areas. The exact cause is not fully understood, but it is thought to involve the immune system mistakenly attacking muscle tissue in a limited area. The main symptoms include a n
How is Focal myositis inherited?
Focal myositis follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Focal myositis typically begin?
Typical onset of Focal myositis is adult. Age of onset can vary across affected individuals.
Which specialists treat Focal myositis?
6 specialists and care centers treating Focal myositis are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.