Signals Tell the Story When Coding Evoked Potential Studies
Remember to look for other services during these encounters. An evoked potential (EP) study asks a simple question: When the nervous system is given a controlled stimulus, does the signal arrive where it should, when it should, and at the strength it should? The answer tells the physician whether a sensory or motor pathway is intact. The coding looks just as simple, but the 95925 (Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in upper limbs) through 95939 (Central motor evoked potential study (transcranial motor stimulation); in upper and lower limbs) range carries a few rules that quietly drive denials: combined-limb codes that replace the single-limb pairs, a bilateral default that turns a one-sided study into a reduced service, and a professional/technical split that shapes the whole claim. Read on for the information you’ll need to code your EP studies. Recognize What the Study Measures During an EP study, the recording equipment delivers the same stimulus many times and averages the responses, separating the evoked waveform from background activity. The resulting peaks have measurable latencies (how long the signal took to arrive) and amplitudes (how large the signal was). Compared against normative data, those values reveal whether conduction is normal, slowed, or blocked. Two pathways matter here, and they run in opposite directions. A short-latency somatosensory EP interrogates the ascending sensory route: A peripheral nerve or skin site is stimulated, and the response is recorded as it climbs through the central nervous system. A central motor EP interrogates the descending motor route: The motor cortex is stimulated transcranially, and the compound muscle action potential is recorded from a target muscle, yielding a central motor conduction time. Somatosensory studies stimulate the periphery and record centrally to test sensory conduction, while central motor studies stimulate centrally and record peripherally to test motor conduction. That contrast is the whole distinction between the studies, and it is the first thing the documentation needs to make clear. E/M Usually Precedes EP EP studies are not screening tools. They belong in the record once the physician performs an evaluation and management (E/M) service (office/outpatient, inpatient, consultation) and identifies a specific pathway worth questioning. Recognized indications across Medicare coverage articles include suspected or established multiple sclerosis, spinal cord trauma, nontraumatic myelopathy such as cervical spondylotic myelopathy, spinocerebellar and other degenerative disorders, subacute combined degeneration, syringomyelia, and assessment of pathway integrity in coma. Central motor studies in particular earn their place when upper motor neuron signs, such as weakness paired with spasticity and hyperreflexia, point to the descending motor pathway. Medical necessity rests on the following: a documented deficit, a suspected lesion, and a question the result will help answer. Learn How the Codes Are Built Code selection turns on the pathway tested and the region studied. Consider this chart: Study Region Code Short-latency somatosensory EP Upper limbs 95925 Lower limbs 95926 Trunk or head 95927 Upper and lower limbs 95938 Central motor EP (transcranial) Upper limbs 95928 Lower limbs 95929 Upper and lower limbs 95939 Two rules account for most errors in this range. The combined-limb rule comes first: When both upper and lower limbs are tested in one session, the combined code is the single correct code. Report 95938 (Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in upper and lower limbs) instead of 95925 plus 95926 (… in lower limbs), and 95939 instead of 95928 (Central motor evoked potential study (transcranial motor stimulation); upper limbs) plus 95929 (… lower limbs) — never the pairs together. The bilateral default comes second. The somatosensory codes (95925, 95926, 95927 [Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in the trunk or head], 95938) are defined as bilateral studies. Under longstanding American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) guidance, a somatosensory study performed on only one side should carry modifier 52 (Reduced services) for reduced services. Billing a unilateral study at full value is an avoidable audit finding. One boundary is worth naming, because the numbering invites confusion: the same span also holds the visual evoked potential code 95930 (Visual evoked potential (VEP) checkerboard or flash testing, central nervous system except glaucoma, with interpretation and report) and the blink reflex code 95933 (Orbicularis oculi (blink) reflex, by electrodiagnostic testing). Those are different studies. The central motor codes are specifically 95928, 95929, and 95939. Look for Other Services on EP Encounters An EP study rarely travels alone. If the physician studies a second pathway on the same day, you’ll choose from the following codes: Nerve conduction studies and needle electromyography often round out the workup and are reportable when distinct, supported, and in line with National Correct Coding Initiative (NCCI) edits. Report these services with the following codes, as appropriate: Additionally, the professional/technical split runs through all of it: modifier 26 (Professional component) for interpretation only, TC (Technical component) for the technical component only, and no modifier when one entity furnishes both. The encounter might also warrant reporting a significant, separately identifiable evaluation and management (E/M) service with modifier 25 (Significant, separately identifiable evaluation and management service by the same physician or other qualified health care professional on the same day of the procedure) appended. The relationship that confuses coders most often is baseline study versus intraoperative monitoring. When EPs establish baseline data before surgical neuromonitoring, the baseline study (95925-95939) and the monitoring time are significant, separately reportable services. You can capture monitoring with: Per Centers for Medicare & Medicaid Services (CMS) policy, monitoring time excludes setting up, recording, and interpreting the baseline studies and removing electrodes, which keeps the two services cleanly distinct. Check Documentation for These Elements Every reporting decision traces back to the operative report. It should open with the indication and the suspected pathway lesion, then state the study type and the regions tested — because somatosensory versus central motor and upper versus lower versus combined limbs is exactly what separates the codes. The combined code is defensible only when the record names all four limbs. From there, the report should capture the nerves stimulated, the recording sites, the latencies and amplitudes obtained, and an interpretation against normative values that ties the findings back to the clinical picture. Any modifier needs its own support: a documented reason only one side was studied for modifier 52, and a clear interpretation-only role for modifier 26. You cannot bill the professional component (modifier 26) without a signed, dated report. Two errors surface in audits of EP studies more than any others: Reporting 95925 and 95926 together when 95938 was the correct code, and billing a unilateral somatosensory study at full value when modifier 52 was required. A record that names the limbs tested and the laterality of the study will help with those potential hurdles. Jennifer McNamara, CPC, CVBA, CRC, CPMA, CDEO, CEMA, COSC,
CGSC, COPC, CPC-I, Contributing Writer
