Differential Diagnosis for Neurologic Findings

The patient's symptoms of leg weakness, dry eyes and mouth, weight loss, and mild ptosis, along with the absence of reflexes and difficulty rising from a chair, suggest a complex neurologic condition. The presence of a mass in the right hilum on the x-ray film adds a critical component to the diagnosis, potentially linking the neurologic findings to a systemic or paraneoplastic condition.

• Single Most Likely Diagnosis:

  • C) Peripheral nerve: The patient's symptoms such as leg weakness, absent reflexes, and difficulty rising from a chair, in the context of a mass in the right hilum, could suggest a paraneoplastic syndrome affecting the peripheral nerves, such as paraneoplastic neuropathy associated with small cell lung cancer (given the patient's long history of smoking and the presence of a hilar mass).

• Other Likely Diagnoses:

  • D) Presynaptic neuromuscular junction: Conditions like Lambert-Eaton Myasthenic Syndrome (LEMS) could explain the proximal muscle weakness, reduced or absent reflexes, and autonomic symptoms like dry mouth. LEMS is often associated with small cell lung cancer, which could be suggested by the hilar mass.
  • A) Muscle membrane: Myasthenia gravis, an autoimmune disease affecting the neuromuscular junction at the muscle membrane, could present with muscle weakness and ptosis. However, it less commonly presents with systemic symptoms like significant weight loss and is less directly linked to lung masses.

• Do Not Miss Diagnoses:

  • Sympathetic or Parasympathetic nervous system involvement: While less likely given the primary symptoms, conditions affecting these systems could have severe consequences. For example, paraneoplastic autonomic neuropathy could lead to significant autonomic dysfunction, including orthostatic hypotension, which could be life-threatening.

• Rare Diagnoses:

  • E) Sympathetic nervous system: Direct involvement of the sympathetic nervous system, such as in paraneoplastic syndromes affecting sympathetic pathways, is less common but could explain some autonomic symptoms.
  • B) Parasympathetic nervous system: While the dry eyes and mouth could suggest parasympathetic dysfunction, a primary condition affecting the parasympathetic nervous system is less likely given the broader neurologic and systemic symptoms presented.