Differential Diagnosis for New Thigh Weakness and Hypereflexia at Knee

• Single most likely diagnosis:
  • Amyotrophic Lateral Sclerosis (ALS): This condition is characterized by progressive muscle weakness and hypereflexia due to the involvement of upper and lower motor neurons. The thigh weakness and hypereflexia at the knee could be initial manifestations of ALS, making it a prime consideration.
• Other Likely diagnoses:
  • Multiple Sclerosis (MS): MS can cause a wide range of neurological symptoms, including weakness and reflex changes. The optic spinal form of MS, in particular, might present with lower limb symptoms.
  • Spinal Cord Compression: Compression of the spinal cord, often due to a herniated disk, tumor, or other space-occupying lesion, can lead to weakness and reflex abnormalities below the level of compression.
  • Peripheral Neuropathy: Certain types of peripheral neuropathy, especially those affecting the proximal nerves (like diabetic amyotrophy), can cause thigh weakness. However, hypereflexia is less common in pure peripheral neuropathies.
• Do Not Miss diagnoses:
  • Spinal Epidural Abscess: This is a medical emergency that can cause rapid progression of neurological deficits, including weakness and reflex changes. Prompt diagnosis and treatment are crucial to prevent permanent damage.
  • Cauda Equina Syndrome: A condition where the nerves in the spinal canal are compressed, leading to low back pain, sciatica, and potentially severe neurological deficits, including weakness and loss of reflexes in the lower limbs.
  • Guillain-Barré Syndrome: An autoimmune disorder that can cause rapid-onset muscle weakness and areflexia (not hypereflexia initially), but it's crucial to consider due to its potential for respiratory failure and the need for early treatment.
• Rare diagnoses:
  • Tick-borne illnesses (e.g., Tick Paralysis): Certain tick-borne diseases can cause ascending paralysis, which might initially present with thigh weakness.
  • Inherited Neuropathies (e.g., Charcot-Marie-Tooth disease): While these conditions typically present with distal weakness and areflexia, some forms can have a more proximal involvement and variable reflex changes.
  • Neuromuscular Junction Disorders (e.g., Myasthenia Gravis): These conditions primarily cause fluctuating muscle weakness, and while they can affect proximal muscles, they are less likely to cause hypereflexia.