Myalgias and myositis: Pathology review


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Myalgias and myositis: Pathology review


Pediatric musculoskeletal conditions

Radial head subluxation (Nursemaid elbow)

Developmental dysplasia of the hip

Legg-Calve-Perthes disease

Slipped capital femoral epiphysis

Transient synovitis

Osgood-Schlatter disease (traction apophysitis)

Musculoskeletal injuries and trauma

Rotator cuff tear

Dislocated shoulder

Radial head subluxation (Nursemaid elbow)

Winged scapula

Thoracic outlet syndrome

Carpal tunnel syndrome

Ulnar claw

Erb-Duchenne palsy

Klumpke paralysis

Iliotibial band syndrome

Unhappy triad

Anterior cruciate ligament injury

Patellar tendon rupture

Meniscus tear

Patellofemoral pain syndrome

Sprained ankle

Achilles tendon rupture



Degenerative disc disease

Spinal disc herniation


Compartment syndrome


Bone disorders

Osteogenesis imperfecta


Pectus excavatum


Genu valgum

Genu varum

Pigeon toe

Flat feet

Club foot

Cleidocranial dysplasia



Bone tumors




Osteomalacia and rickets


Paget disease of bone


Lordosis, kyphosis, and scoliosis

Joint disorders



Spinal stenosis

Rheumatoid arthritis

Juvenile idiopathic arthritis


Calcium pyrophosphate deposition disease (pseudogout)

Psoriatic arthritis

Ankylosing spondylitis

Reactive arthritis


Septic arthritis


Baker cyst

Muscular disorders

Muscular dystrophy



Inclusion body myopathy

Polymyalgia rheumatica



Neuromuscular junction disorders

Myasthenia gravis

Lambert-Eaton myasthenic syndrome

Other autoimmune disorders

Sjogren syndrome

Systemic lupus erythematosus

Mixed connective tissue disease

Antiphospholipid syndrome

Raynaud phenomenon


Limited systemic sclerosis (CREST syndrome)

Musculoskeletal system pathology review

Back pain: Pathology review

Rheumatoid arthritis and osteoarthritis: Pathology review

Seronegative and septic arthritis: Pathology review

Gout and pseudogout: Pathology review

Systemic lupus erythematosus (SLE): Pathology review

Scleroderma: Pathology review

Sjogren syndrome: Pathology review

Bone disorders: Pathology review

Bone tumors: Pathology review

Myalgias and myositis: Pathology review

Neuromuscular junction disorders: Pathology review

Muscular dystrophies and mitochondrial myopathies: Pathology review

Pediatric musculoskeletal disorders: Pathology review


Myalgias and myositis: Pathology review

USMLE® Step 1 questions

0 / 6 complete


USMLE® Step 1 style questions USMLE

of complete

A 41-year-old woman is evaluated by the outpatient physician for 5-months of generalized fatigue and diffuse soft-tissue pain. The pain is present in the upper extremities, lower extremities, and back. She feels tired every morning despite getting adequate sleep in the evening. Past medical history is notable for hypertension that is currently managed with propranolol. Temperature is 37.2°C (98.9°F), blood pressure is 136/88 mmHg, pulse is 61/min, and respiratory rate is 15/min. Physical examination reveals 5/5 strength and full range-of-motion in the upper and lower extremities. Soft-tissue tenderness is elicited at multiple locations across the patient’s body. Laboratory results are as follows:  

Laboratory value  Result
 Hemoglobin  14.8 g/dL 
 Leukocyte  7,800/mm3 
 Erythrocyte sedimentation rate (ESR)   7 mm/h 
 Serum creatinine kinase  27 U/L 
 Antinuclear antibodies  Negative 

Which of the following additional findings would most likely be found in this patient?


Content Reviewers

Yifan Xiao, MD


Daniel Afloarei, MD

Sam Gillespie, BSc

Victoria Cumberbatch

Ursula Florjanczyk, MScBMC

On your rounds, you see two individuals. First is Yu Yan, a 58-year-old female who presents with a 2-week history of fatigue, weight loss, fevers, and bilateral pain with stiffness in the shoulder and hip girdles. These symptoms are worse at night and last for more than an hour. She also mentions that she finds it hard to get out of bed in the morning due to stiffness. On examination, her wrists and finger joints are painful and swollen, but there’s no muscle weakness. Then you see Elizabeth, a 38-year-old female who has a 4-year history of body pain. The pain was initially limited to her neck, but it has gradually spread and she now complains of constant pain all over. She does not sleep well and is chronically fatigued. Examination revealed many tender points throughout her body but no sign of joint swelling or muscle weakness. Blood tests were performed in both. In Yu Yan’s case, there was an increase in inflammatory markers, but creatine kinase levels were normal. In Elizabeth’s, blood tests were completely normal.

Both people have myalgias, or muscle pain. There are many causes but let’s start with myopathies, which are neuromuscular disorders in which the primary symptom is muscle weakness due to muscle cell dysfunction. There are two main inflammatory myopathies, polymyositis and dermatomyositis.

First, polymyositis is an autoimmune disease where there’s inflammatory infiltration in striated muscles that cause muscle damage. Now, the cause is still unknown, but polymyositis is often associated with other autoimmune diseases, including Sjogren syndrome, rheumatoid arthritis, scleroderma, and mixed connective tissue disease. It is thought that there’s an overexpression MHC class I molecules and muscular autoantigens, which end up triggering a primarily cell-mediated immune response that inappropriately activates CD4+ and CD8+ T-cells. This is probably due to molecular mimicry, which is when an immune cell mistakes a protein in the body as being foreign due to their similar structure. Sometimes, humoral immunity can also kick in when B-cells get activated by the autoantigens and make antibodies against them. These include histidyl-tRNA synthetases, also called Jo-1; a helicase protein known as Mi-2; and components of the signal-recognition particle, or SRP for short, which helps with protein trafficking within the cell. The bottom line is that these two immune reactions result in inflammation in and around the muscles that are being attacked, attacks which occur repeatedly over time, and can involve different muscle groups.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
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  5. "Clinical presentation and evaluation of dermatomyositis" Indian Journal of Dermatology (2012)
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  7. "Inflammatory Muscle Diseases" New England Journal of Medicine (2015)
  8. "Polymyalgia rheumatica" BMJ (2013)

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