Differential Diagnosis for Proximal Muscle Weakness

Single Most Likely Diagnosis

• Polymyalgia Rheumatica (PMR): This condition is characterized by aching and stiffness in the neck, shoulder, and hip areas, which is often accompanied by proximal muscle weakness. It is a common cause of proximal muscle weakness, especially in individuals over the age of 50.

Other Likely Diagnoses

• Thyroid Disorders (Hypothyroidism or Hyperthyroidism): Both hypothyroidism and hyperthyroidism can cause muscle weakness, including proximal muscle weakness. Thyroid function tests can help diagnose these conditions.
• Diabetes Mellitus: Diabetes can cause proximal muscle weakness due to various mechanisms, including neuropathy and myopathy.
• Osteomalacia or Rickets: These conditions, caused by vitamin D deficiency, can lead to proximal muscle weakness due to the role of vitamin D in muscle function.
• Chronic Kidney Disease: Muscle weakness, including proximal muscle weakness, can be a symptom of chronic kidney disease due to electrolyte imbalances and other metabolic disturbances.

Do Not Miss Diagnoses

• Guillain-Barré Syndrome: An autoimmune disorder that can cause rapid onset of muscle weakness, including proximal muscles. It is a medical emergency requiring prompt treatment.
• Lambert-Eaton Myasthenic Syndrome (LEMS): A rare autoimmune disorder that can cause proximal muscle weakness, among other symptoms. It is often associated with small cell lung cancer.
• Myasthenia Gravis: An autoimmune disease that leads to fluctuating muscle weakness, including proximal muscles, which worsens with activity and improves with rest.

Rare Diagnoses

• Dermatomyositis and Polymyositis: These are inflammatory myopathies that can cause proximal muscle weakness, skin rash (in dermatomyositis), and other systemic symptoms.
• Inclusion Body Myositis: A slowly progressive inflammatory muscle disease that affects both proximal and distal muscles, more common in men over 50.
• Mitochondrial Myopathies: A group of disorders caused by mitochondrial dysfunction, leading to muscle weakness, including proximal muscles, and other systemic symptoms.
• Pompe Disease: A genetic disorder caused by the deficiency of acid alpha-glucosidase, leading to glycogen accumulation in muscles and causing proximal muscle weakness, among other symptoms.