Muscle weakness and Myalgia

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Differential Diagnosis of Muscle Weakness and Myalgia

Organ system	Disease	Symptoms												History	Physical Examination	Diagnosis
		Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	Laboratory Findings			Creatine Kinase	Muscle Biopsy	Electromyogram
Medication−induced	Corticosteroids	Variable	Proximal	−	+	−	−	−	+	−	−	Central obesity Excessive sweating Insomnia Reduced libido  Amenorrhea Infertility  Psychological disturbances	Positive h/o medications	Facial and sphincter muscles are usually spared	Positive ACTH stimulation test 24-hour urine cortisol Low dose dexamethasone suppression test	Normal	Normal	Normal
	Statins	60+	Proximal	−	+	−	−	−	−	−	−/+(Rhabdomyolysis)	N/A	Positive h/o medications H/o other medication use	Tenderness Muscle aches	↑↑ Liver enzymes	↑↑	Necrosis Degeneration, and regeneration of fibers Phagocytic infiltration	Normal
Endocrine	Adrenal insufficiency	30−50 years	Proximal	−	+	−	−	−	−	+	−	Signs of glucocorticoid, mineralocorticoid, and, androgen deficiency	Signs of postural hypotension History of tuberculosis History of malignancy History of other autoimmune disease	Hypotension  Hyperpigmentation  Auricular−cartilage calcification  Vitiligo	Electrolyte abnormalities Hypoglycemia	Normal	Normal	Normal
	Hypothyroidism	55	Proximal	−	+	+	−	−	+	+	+ Rhabdomyolysis	Signs of hypothyroidism	H/o weight gain	Myxoedema  Muscle pseudohypertrophy	Increased TSH	↑↑	Nonspecific	Normal
	Diabetic infraction	45	Proximal	+	+	−	−	+	+	−	−	Cramps Sudden onset of pain Anterior thigh muscles are most commonly involved	H/O long standing diabetes	Swelling Tenderness	Elevated ESR Leukocytosis	Normal	Necrosis Edema	Normal
Organ system	Disease	Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	History	Physical Examination	Laboratory Findings	Creatine Kinase	Muscle Biopsy	Electromyogram
Inflammatory/ Rheumatologic	Dermatomyositis	40s−50s Can affect children	Proximal	+	+	−	−	−	−	+	−	Rash Dyspnea Weight loss Cough	Viral infections Cancer	Heliotrope rash on face and hands Telangiectasia Erythema Mechanic's hands Gottron's sign ( violaceous scaly eruption )	↑↑ ESR ↑↑ CRP	↑↑	Perimysial mononuclear infiltrate	Myopathic
	Polymyositis	> 18 years	Proximal	+	+	−	−	−	−	+	−	Similar to dermatomyositis without mucous and skin involvement	N/A	N/A	↑↑ ESR ↑↑ CRP	↑↑	Endomysial mononuclear infiltrate Patchy necrosis
	Polymyalgia Rheumatica	50s	Diffuse	+	+	−	−	−	−	+	−	Weight loss	History of joints stiffness, worse in the morning	Restricted shoulder motion	↑↑ ESR ↑↑ CRP	Normal	Normal	Normal
Genetic	Limb−girdle muscular dystrophies	<15 yrs	Proximal	−	+	+	+	−	+	−	−	Calf hypertrophy Scapular winging Cardiomyopathy Cardiac arrhythmias Respiratory muscle weakness	Autosomal dominant Deterioration of ability to run/walk	Muscle weakness is generally symmetric	LMNA gene CAV3 gene	↑↑	N/A	Myopathic
Organ system	Disease	Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	History	Physical Examination	Laboratory Findings	Creatine Kinase	Muscle Biopsy	Electromyogram
Infectious	Lyme disease	Variable	Proximal	+	+	−	+/−	+	−	−	−	Erythema Migrans Flu−like symptoms Lyme arthritis Neurological manifestations	H/o tick bite Hiking trip	Target−like lesions HSM	Clinical diagnosis +Serology	N/A	N/A	N/A
	Influenza	Variable	Proximal and Distal	+	+	−	+	−	−	−	+	Fever Malaise Rhinorrhea Muscle pain worse with movement	Cold weather H/o Ill contacts	Muscle weakness, tenderness, and swelling.	↑↑ Liver enzymes Positive PCR	↑↑	N/A	N/A
	Pyomyositis	Variable	Proximal & Distal	+	+	−	−	−	−	+	−	Fever Malaise Psoas abscess	Immunocompromised	Muscles are painful, swollen, tender, and indurated. Depending on the site of involvement, it may mimic appendicitis (psoas muscle), septic arthritis of the hip (iliacus muscle), or epidural abscess (piriformis muscle).	Leukocytosis Elevated ESR	N/A	N/A	N/A