digital current monitor/sensor for monitoring ~0.1 uA to mA current from a MCU and sensor
Current consumption over a time period suggests voltage-to-frequency or current-to-frequency conversion. Current spikes will be integrated into frequency over short time periods, while any microcontroller can collect frequency in its counter/timer. Count overflows can be extended to whatever lengths are needed in software.

The Texas Instruments application note AN240 suggests some circuits:


  AN-240 Wide-Range Current-to-Frequency Converters (Rev. B)


http://www.ti.com/lit/an/snoa594b/snoa594b.pdf