instruction: provide the number of patients diagnosed with unspecified encephalopathy who had spinal tap lab test.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN procedures ON demographic.hadm_id = procedures.hadm_id WHERE diagnoses.long_title = "Encephalopathy, unspecified" AND procedures.short_title = "Spinal tap"