Differential Diagnosis for Severe Proximal Weakness
Single Most Likely Diagnosis
- Polymyositis/Dermatomyositis: These are inflammatory muscle diseases that commonly present with symmetric proximal muscle weakness, which can be severe. The presence of skin manifestations in dermatomyositis can help differentiate it from polymyositis.
Other Likely Diagnoses
- Muscular Dystrophies: Conditions like Duchenne muscular dystrophy and Becker muscular dystrophy can present with progressive proximal muscle weakness, although the onset is typically in childhood.
- Thyroid Disorders: Both hypothyroidism and hyperthyroidism can cause muscle weakness, with hypothyroidism more commonly associated with proximal muscle weakness.
- Diabetic Amyotrophy: A condition associated with diabetes that causes severe proximal muscle weakness, typically affecting one side more than the other.
- Steroid Myopathy: Long-term use of corticosteroids can lead to proximal muscle weakness.
Do Not Miss Diagnoses
- Guillain-Barré Syndrome: An autoimmune disorder that can cause rapid onset of muscle weakness, which can be severe and proximal. It's crucial to diagnose early due to the potential for respiratory failure.
- Botulism: A rare but potentially life-threatening condition caused by a toxin that can lead to muscle weakness, including proximal muscles, along with other symptoms like blurred vision and difficulty swallowing.
- Spinal Cord Compression: Conditions like tumors or abscesses compressing the spinal cord can cause rapid onset of muscle weakness, which may be proximal, along with sensory deficits and autonomic dysfunction.
Rare Diagnoses
- Mitochondrial Myopathies: A group of disorders affecting the mitochondria that can cause muscle weakness, among other symptoms. Proximal muscle weakness can be a feature, but these conditions are rare and often have additional systemic manifestations.
- Inclusion Body Myositis: The most common acquired myopathy in adults over 50, characterized by progressive muscle weakness and wasting, particularly affecting the proximal muscles, but it tends to be more insidious and asymmetric.
- Limb-Girdle Muscular Dystrophy: A diverse group of genetic disorders characterized by progressive muscle weakness, primarily affecting the proximal muscles around the shoulders and hips. The onset and severity can vary widely.