Pins & needles in left hand?

Many possible causes: Several things can cause this. Most common is probably carpal tunnel syndrome but perhaps a pinched nerve in your neck (from a herniated disc or rarely a tumor) or peripheral neuropathy caused by diabetes, heavy metal toxicity, other toxins or Vit B12 deficiency. You need to see a doctor (ideally a neurologist but a good internist or family doctor could help) to determine the cause and treatment.

Pins and needles.: General considerations would be a neurological or vascular cause. Carpal tunnel syndrome? Cervical radiculopathy? Raynaud’s? A local evaluation and directed testing would be wise.