Use of Laboratory Tests in the Evaluation of Pain

1. Use of Laboratory Tests in the Evaluation of Pain Alfredo Romero, MD

2. The Basic Pain Laboratory Battery CBC Acute phase proteins: ESR, CRP Blood Chemistry: Glucose, NA, K, CL, HCO3, CA, BUN, Crt, Uric acid, total protein, albumin, globulin, bilirubin Enzymes: Alkaline phosphatase, CK, LDH, AST, ALT Thyroid: TSH, Free T4 Vitamin B12 Labs depend on the clinical situation.

3. Complete Blood Count RBC: Anemia Hgb <13g/dL for men, <11d/dL women. ?Reticulocyte count: Index of bone marrow activity. Elevated in Hemolytic anemia. Normal: 0.5-2.5% ?HbS: Heterezygous state� sickle trait (SA). Pt asymptomatic. Homozygous state, sickle cell disease . Screening tests does not distinguish between SSD and SA. Definitive Diagnosis require Hgb electrophoresis. WBC: Bacterial infection: leucocytosis with increased percentage of neutrophils and bands, but overwhelming infection in debilitated, elderly patients may fail to show leucocytosis. ?Drug-induced agranulocytosis: WBC < 4000may be caused by dilantin, carbamazepine, and NSAIDS. Platelets: Severe thrombocytopenia <50.000, Thrombocytosis >900.000. Drug-induce thrombocytopenia: heparin, furosemide, cimetidine, quinine.

4. Electrolytes Na: Hyponatremia: Symptoms such as nausea, malaise, lethargy, psychosis, seizures generally occur with Na < 120 mEq/L. Check diuretics, but also could caused by carbamazepine. K: Hyperkalemia usually associated with renal failure, but drugs like B-blocker, potassium-sparing diuretics, NSAIDS, and cyclosporine could cause it.

5. Common Connective Tissues Diseases and Vasculitis Connective Tissue Diseases Systemic lupus erythematosus (SLE) Mixed connective tissue disease Primary Sjogren�syndrome Rheumatoid arthritis Progressive systemic sclerosis (scleroderma) Polymyositis and dermatomyositis Vasculitis Polyarteritis nodosa Wegener� granulomatosis Temporal arteritis Behcet�s disease

6. Connective Tissue Diseases SLE: ANA is the most sensitive test. Titers above 1:80 are considered positive, but a positive result is not sufficient for diagnosis. ANA titers can be seen in multiple conditions like hepatitis, malaria, other connective tissue disorders and thyroid disease. RA: The most important rheumatoid factor is an IgM macroglobulin. Sensitivity of RF is 70% to 90%. Also can be seen in others conditions like SLE, scleroderma, dermatomyositis, hepatitis.

7. Serologic Testing for Collagen Vascular disorders Rheumatoid Factor: 80% sensitivity in RA ANA: titer >1:320 have 95% specificity for SLE ANCA: 90% positive in Wegener�s granulomatosis Anti-Ro antibodies: 70% positive in Sjogren�s syndrome Antinuclear (nuclear RNA): 60%-90% positive in scleroderma Anti-SM: Highly specific for SLE Anti-centromere: Suggest CREST

8. Thyroid Tests Thyroid dysfunction may be confused with dementia First check TSH If THS is normal no further test is necessary If TSH is abnormal check fee thyroxine (T4)

9. Prostatic Specific Antigen (PSA) Can detect prostate cancer 3 to 5 years before clinical symptoms appear PSA is very specific for prostate disease, but no necessarily for prostate cancer Can be positive in BPH, acute bacterial prostatitis, after cystoscopy, and even use of exercise bicycles.

10. Human Immunodeficiency Virus Patient may present with abdominal pain, painful neuropathies, oral cavity pain, headache, reactive arthritis, and post herpetic neuralgia. Seroconversion generally occurs 6 to 10 weeks after infective exposure Enzyme immunoassay testing for initial screening. Confirmatory test is Western Blot Therapy goal is to keep viral load >10.000 Generally patient is asymptomatic with CD4 level above 500

11. Spirochetal Diseases Two �great imitators� Syphilis: Caused by Treponema pallidum. ?Initial screening with non-treponemal test: VDRL and rapid plasma reagin (RPR). ?Confirmatory test : specific treponemal test. FTA-ABS Lyme Disease: Caused by Borrelia burgdorferi which infects Ixodes dammini ticks. ?Laboratory evaluation is appropriate for patients with characteristic arthritic, neurologic, or cardiac symptoms ?Positive ELISA test should be confirmed by a Western blot.

12. Neuropathy Diabetes and alcoholism are the most common cause of peripheral neuropathy in USA. Other causes are amyloidosis, AIDS, PN, SLE, malignancy, myeloma, arsenium, lead, Vit B12 deficiency. Level of Vit B12 < 200ng/L are abnormal. Look for elevated serum gastrin, intrinsic factor-antibody blocking antibodies. Shilling�s test may be necessary

13. Neuropathy Paraneoplastic neuropathy should be suspected in middle-aged patient, heavy smoker, c/o tingling and painful numbness all over. One indicator is serum antineuronal nuclear antibodies type I (ANNA:anti-HU). Urine level .25 mg/d of arsenium are abnormal unless seafood was eaten recently Lead neuropathy present with anemia, urine lead level >0.2mg/L. Blood lead levels can be misleading

14. Uric acid Hyperuricemia is defined by a serum uric acid concentration >7mg/dL. 10% of gout patients may have normal levels Many patients with hyperuricemia never experience a gout attack Diagnosis is made with demonstration of uric acid crystals in the synovial fluid of an acutely inflamed joint

15. Liver Function Tests Only serum albumin, bilirubin, and PT provide useful information on how efficiently the liver is actually working Normal LFT do not ensure a normal liver The most common marker of hepatic injury are aspartate aminotransferase (AST) and alanine amonotransferase (ALT). Slight elevations of these enzymes may not indicate liver disease. AST and ALT are found in skeletal muscle as well. Alkaline phosphate (ALP) and gamma-glutamyltransferase are elevated with intra or extra-hepatic cholestasis Serum ALP also originates from bone. Serum conjugated bilirubin does not become elevated until liver has lost half of its excretory capacity. Ammonia concentrations correlate poorly with the degree of confusion

16. Therapeutic Drug Monitoring and Testing for Drugs of Abuse Medications such as phenobarbital, valproic acid, carbamazepine, phenytoin, lithium carbonate, and triclyclic antidepressants have readily available assays. Particularly in elderly patients, toxicity may occur at level normally considered therapeutic Urine can be positive for cannabinoids several days after a single use of marijuana Cocaine may be detectable for several weeks after cessation in heavy users A positive result for amphetamines in the urine implies use within the last 24 to 48 hours.

17. Magnetic Resonance Technology Depicts anatomic sections in tomographic slides of varying thickness It is based on the effects that a large magnetic field and radiofrequency (RF) pulses have on the nuclei of hydrogen atoms in body tissues. Hydrogen nuclei can be made to align in large magnetic fields. This alignment is perturbed with radiopulses. When this RF is terminated, the nucleus attempt to realign giving off energy that can be detected. The time it takes for the voltage to decay is expressed by two times constant the T1 and T2

18. Advantages of MRI Has no known adverse biologic effects MRI does not use ionizing radiation Produces substantially greater tissue contrast resolution Provides significantly more information than CT about tissue characteristics Beam-hardening artifacts seen with CT(e.g posterior fossa) do not occur with MRI MRI has multiplanar capability Define subacute an chronic collections of blood MRI does not use iodinated contrast material (can be used in patients allergic to iodine).

19. Indications and Contraindications Indications: MRI is the imaging of choice for the evaluation of nearly all abnormalities involving brain, spine and musculoskeletal system (outstanding modality for evaluating various joints) Contraindications: Cardiac pacemaker, ferromagnetic cerebral aneurysm clips, metallic foreign body near the eye, and cochlear implants Limitations: Inability to demonstrate exquisite bone detail and calcification, long imaging times, limited availability in certain areas, expense study, and some patients experience claustrophobia.

20. Radionuclide Scanning Scintigraphy detects the distribution in the body of a radioactive agent injected into a vein The strength of this test resides in its ability to portray the functional status of an organ or body part The radioactivity is detected from outside the body with special gamma cameras Localized defects that cause either too much or too little radioactivity to be emitted from a usually homogeneous area are then detected as pathologic lesions

21. Bone Scanning Technetium Tc 99m is an ideal isotope for bone scanning Bone scan is a map of osteoblastic activity Areas of increased or decreased bone turnover or remodeling can be identified It is commonly use to detect metastatic disease, stress or fatigue fracture, , early detection of acute osteomyelitis or reactivation of the chronic form

22. Others Radionuclide Scanning Tests Thallium myocardial imaging: For CAD Ventilation-Perfusion scanning: (V/Q scan) for Pulmonary embolism Iodine 125-labeled fibrinogen scanning: The most sensitive noninvasive test to detect early calf DVT.

23. Ultrasonography The ultrasound transducer converts electrical energy to high-frequency sound energy that is transmitted into the patient�s tissue. The transmitted pulse encounters tissue interfaces that reflect a portion of the ultrasound beam back to the transducer. US is severely limited by bone and by structures, such as bowel and lung, that contain gas. US is very useful in evaluating liver, gallbladder, kidney, ureteres, urinary bladder, pancreas, pelvic organs, thyroid, and cystic masses of the extremities Doppler US is 84% sensitive in detecting DVT above the knee.

24. Contrast-Enhanced Examinations Arthrography: Imaging after injection of contrast material into a joint space. Effective in demonstrating rotator cuff injuries, adhesive capsulitis, ligamentous injuries. MRI has replaced arthrography. Myelography: Introduction of water-soluble, nonionic contrast agent into the subaracnoid space via lumbar puncture. This procedure is effective and accurate for demonstrating the subarachnoid space, spinal cord, and nerve roots. Almost replaced by MRI

27. Selection of Radiologic Imaging Headache and Orofacial pain ?Acute, severe headache are best imaged by CT ?For subacute or chronic headaches MRI is the procedure of choice. ?Orofacial pain may require dental radiography, temporomandibular pain at require MRI or arthrography. Sinusitis is best evaluated by CT Thorax and Abdomen ?Investigated with CT, US, and contrast studies Neck and Upper Extremities ?Investigated with routine radiography and or MRI

28. Selection of Radiologic Imaging Low Back and Lower Extremity ?MRI is the procedure of choice for screening patients with low back pain ?In asymptomatic adults 30% are found to have a mayor abnormality on MRI. ?Generally a bulging disc is not associated with sciatica, whereas protruded disc is. CT myelography, is often the best and definitive diagnostic modality for arachnoiditis and epidural fibrosis.