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Clausen's Butterfly Chart - ENT MS University Exam Guide
What It Is
Clausen's (Claussen's) Butterfly Chart is a graphical method of representing bithermal caloric test results using Electronystagmography (ENG). Introduced by Prof. C.F. Claussen, it provides a simple pictorial representation of ENG caloric data that can be understood by both clinicians and patients - compared to raw ENG tracings which are complex to interpret.
Background - The Bithermal Caloric Test
The test uses the Fitzgerald-Hallpike method (1942):
- Patient lies supine with head at 30 degrees (brings lateral semicircular canal into vertical plane)
- Ear irrigated with:
- Cold water: 30°C (cold stimulation)
- Warm water: 44°C (warm stimulation)
- 40 ml irrigated over 40 seconds
- Duration of induced nystagmus (or culmination frequency in ENG) is measured
- Mnemonic for nystagmus direction: COWS - Cold Opposite, Warm Same
Four irrigations are performed: Right Warm (RW), Right Cold (RC), Left Warm (LW), Left Cold (LC)
Construction of the Butterfly Chart
The chart has 4 quadrants, each representing one of the four caloric reactions:
Left Cold | Right Warm
(LC) | (RW)
-----------+-----------
Left Warm | Right Cold
(LW) | (RC)
- Abscissa (X-axis): Time in culmination phase (1 mm = 1 second, spans 30 seconds)
- Ordinate (Y-axis): Number of nystagmus beats / culmination frequency (1 mm = 1 beat)
- A normal range band is marked on the Y-axis of each quadrant
- The plotted shape of responses across all 4 quadrants resembles a butterfly - hence the name
Trinary Coding System
Each caloric response is assigned one of three digits based on where it falls relative to the normal range:
| Code | Meaning | Response |
|---|---|---|
| 0 | Normal | Within normal range |
| 1 | Hypoactive | Below normal range (reduced response) |
| 2 | Hyperactive | Above normal range (exaggerated response) |
The four digits are written in the order: RW - RC - LW - LC
This gives a 4-digit trinary code (e.g., 0000, 1100, 2020)
Theoretically, 81 combinations (3^4) exist; Claussen's database of 10,335 patients found 68 codes in practice.
Key Patterns and Interpretation (Exam High-Yield)
Normal Pattern
| Code | Meaning |
|---|---|
| 0000 | All four responses normal - most common finding (22-43% of cases) |
| 1111 | Minor butterfly - all responses slightly reduced (bilateral mild hypo-function) |
| 2222 | All responses elevated (bilateral hyper-function) |
Peripheral Lesion Patterns
These show canal paresis (unilateral weakness) - one ear responds less:
| Code | Interpretation |
|---|---|
| 1100 | Right canal paresis - both right responses (RW+RC) hypoactive |
| 0011 | Left canal paresis - both left responses (LW+LC) hypoactive |
| 1010 | Right directional preponderance toward left (RW↓, LW↓) |
| 0101 | Left directional preponderance toward right |
- Peripheral pattern: codes like 1100, 0011, 1010, 0101
- Nystagmus enhanced by eye closure (peripheral feature)
- Positional nystagmus: latency, geotropic, direction-fixed, fatigable
Central Lesion Patterns
These show hyperactive or mixed responses suggesting loss of central inhibition:
| Code | Interpretation |
|---|---|
| 2200 | Right hyperactivity only - suggests central lesion |
| 0022 | Left hyperactivity only - suggests central lesion |
| 0110 | Directional preponderance to the right (warm side hyper) |
| 1001 | Directional preponderance to the left |
- Central pattern: codes 2200, 0022, 0110, 1001
- Nystagmus NOT suppressed by fixation (fails fixation suppression test - pathognomonic of central)
- May show: vertical nystagmus, direction-changing nystagmus, bilateral gaze paretic nystagmus, saccadic hypermetria, broken smooth pursuit tracking
Summary of Peripheral vs. Central in Butterfly Chart
| Feature | Peripheral | Central |
|---|---|---|
| Canal paresis codes | 1100, 0011 | Usually absent |
| Typical codes | 1100, 0011, 1010, 0101 | 2200, 0022, 0110, 1001 |
| Responses | Hypoactive (1s) | Hyperactive (2s) |
| Fixation suppression | Present (normal) | Absent (abnormal) |
| Eye closure effect | Nystagmus enhanced | Not enhanced |
| Jongkees canal paresis | >25% (pathological) | Usually normal |
Jongkees' Formulae (Always Asked in Exams)
Canal Paresis (CP) % =
(RW + RC) - (LW + LC)
─────────────────────── × 100
RW + RC + LW + LC
- Abnormal: >20-25% (varies by lab; commonly >25% in Indian ENT practice)
- Indicates which ear is weak
Directional Preponderance (DP) % =
(RW + LC) - (LW + RC)
─────────────────────── × 100
RW + RC + LW + LC
- Abnormal: >22-30%
- Indicates which direction nystagmus predominates
Clinical Significance
- BPPV: Butterfly code = 0000 (normal caloric), but positional test shows geotropic, direction-fixed, fatigable nystagmus with latency
- Meniere's disease: Canal paresis (1100 or 0011) - ipsilateral hypofunction
- Vestibular neuritis: Marked canal paresis (code 1100/0011) with normal audiogram
- Acoustic neuroma (VS): Canal paresis ipsilateral, may have complete areflexia on that side
- Brainstem/cerebellar lesion: Central codes (2200, 0022), fixation suppression failure
Exam Points to Remember
- Chart has 4 quadrants - one per caloric stimulus
- Trinary code order: RW - RC - LW - LC
- 0 = normal, 1 = hypo, 2 = hyper
- 0000 = most common code in any study population
- Peripheral codes have "1s" (hypoactive) typically in one ear's column
- Central codes have "2s" (hyperactive) or mixed patterns
- Sensitivity for central lesions ~75%, specificity ~73%; peripheral sensitivity ~64%
- The chart shape across 4 quadrants resembles a butterfly wing - hence the name
- Developed by Prof. C.F. Claussen as a topographic representation of caloric responses using central culmination frequency
- Only investigation that can lateralize the side of vestibular lesion
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