Paraneoplastic Syndromes

Which paraneoplastic endocrine syndrome results from ectopic production of adrenocorticotropic hormone (ACTH) and is most commonly associated with small cell lung cancer?

Hypertrophic osteoarthropathy as a paraneoplastic syndrome is most commonly associated with which malignancy?

Which paraneoplastic syndrome is most commonly associated with small cell lung cancer and is caused by antibodies against voltage-gated calcium channels?

A 58-year-old male smoker presents with progressive proximal muscle weakness and autonomic dysfunction. Electromyography shows facilitation with high-frequency stimulation. Which is the most common malignancy associated with this paraneoplastic syndrome?

A 65-year-old man with squamous cell carcinoma of the lung presents with progressive ataxia, nystagmus, and dysarthria over 3 months. Serum calcium is 11.2 mg/dL (normal). CSF analysis shows mild lymphocytic pleocytosis. Which investigation is most appropriate to confirm the paraneoplastic etiology?