Acoustic Effects of Lightning

Case Report

Auris'Nasus'Larynx (Tokyo) 20, 285-289 (1993)

ACOUSTIC EFFECTS OF LIGHTNING u.K. SONI, M.S., Bachi MISTRY, M.S., S.V. MALLYA, M.S., D.S. GREWAL, M.S., and Smita VARADKAR* Departments of Otolaryngology and *Audiology and Speech Therapy. The T.N. Medical College and B. Y.L. Nair Ch. Hospital. Bombay--400 008. India

The effects of lightning on the audio vestibular apparatus vary with the degree of injury. This depends on whether the individual is struck directly or indirectly by lightning. We reported two cases where lightning has caused trauma to audiovestibular apparatus and have reviewed the available literature. One patient was struck directly by lightning leading to rupture of the tympanic membrane and a conductive hearing loss. The other patient was struck indirectly via telephone cable and had a mixed hearing loss with tympanic membrane intact. Lightning does not always kill but often causes various audiovestibular lesions. The literature since 1960 has been devoid of reference to this subject. The purpose of this paper is to present two cases from our experience and review the available literature. Lightning causes damage to both, middle ear and inner ear directly, or indirectly by transmission over long distance such as over the telephone network. 1• 2 Lightning is explained as electric discharge between a negatively charged cloud bank and a positively charged object on the earth. It has two phases: (1) The "step-ladder process" which frequently changes direction resulting in zigzag nature of the flash and (2) "A return strike" which emits the greatest light and has an electrical charge of up to 200,000 amperes and an electrical potential of 20 million volts responsible for the damaging effects on life and property.3 CASE REPORTS We had two cases oflightning induced acoustic injury, one directly and other indirectly through the telephone cable. Case I A 50-year-old female came to us with the complaints of hearing impairment, tinnitus, and otorrhoea in the right ear since the last 6 years. Received for publication August 24, 1992 285

286

U. K. SONI, B. MISTRY, S. V. MALLYA, et al

The symptoms started suddenly when the ground nearby was struck by lightning. The patient was unconscious for 1 hr. After regaining consciousness, she found that she could not hear with her right ear and had severe tinnitus. She had superficial skin burns over the right shoulder and chest with charring of clothes. After 1 week, she had a discharge from the right ear. She was treated by a general practitioner until she was referred to us. On E.N.T. examination, there was a dry central perforation in the right ear drum (Fig. 1) and the left ear was normal. On pure tone audiometry there was a moderate conductive hearing loss in the right ear

Fig. I. Illustration of the perforated eardrum in Case I. A, central perforation; B, pars tensa; C, pars ftaccida.

Frequency 250

500

in Ix

Hz 2K

4K

0 CD

10

.!:

20

"0

l-

"'lD

5~

40

:20 50

,2Ul '" ~ .. .J::.

to-

('J'

.f:

r;

Q.I

I

'" "-

60 70

80 90 100 110 120

I I

I

div 30

/"

8K

:

I

.......-4 k I I

I I I I

I I

I

:

,,

: "'!.... II ,, -~

I

: ,,

: , I I

,

Fig. 2. Audiogram of right ear in Case I showing conductive hearing loss due to lightning induced tympanic membrane rupture and the improvement 3 months after a Type I tympanoplasty. 0, air conduction; [, bone conduction; I, before tympanoplasty; II, 3 months after tympanoplasty.

287

ACOUSTIC EFFECTS OF LIGHTNING

Frequency 250

CO

0 ,0

.S

20

Q)~

30

"0

~c.D

500

in Hz 11(

I

I

-,

I

~

.. .c ... II)

~

C>

.f:

0

III

J:

-

60

Q)

70

I I I

·

···

81<

· ·: ·: · I

I

:20 50 CI)

4K I

..J~ 40

.2 (f)

2K

,..

...

r--+-

·· .. ·

80

I

90

I

100 110

I

I

I

I I

IZ O

Fig. 3. Audiogram of right ear in Case II showing sensorineural hearing loss due to indirect trauma to the audiovestibular apparatus. 0, air conduction; [, bone conduction.

and normal in the left. Type I tympanoplasty was done for the right ear and audiogram was repeated after 3 months, which showed improvement in hearing (Fig. 2). In this case, a mild direct trauma due to lightning resulted in unilateral tympanic membrane perforation and conductive hearing loss. Case II A 42-year-old male, railway employee presented with hearing loss bilaterally when he was talking on the telephone at the railway station during a lightning storm. The patient felt giddy and had a sudden blackness in front of his eyes. After 2 days, the right ear started discharging. This symptom stopped after a treatment. On examination, the left ear appeared normal whereas the right ear showed a healed perforation. Audiometry revealed mixed hearing loss in the right ear (Fig. 3). In this case an indirect trauma due to lightning resulted in sensorineural hearing loss. DISCUSSION

Normally, in cases who have survived lightning strokes the most common audiovestibular lesion is tympanic membrane rupture. The various injuries to the ear and temporal bone are: unilateral or bilateral, temporary or permanent hearing loss; rupture of tympanic membrane and Reissner's membrane, middle ear and/or inner ear haematoma, degeneration of the organ of Corti and stria vascularis,

288

U. K. SONI, B. MISTRY, S. V. MALLYA, et al

microscopic fractures in the temporal bone, facial nerve palsy, and/or charring of the temporal bone. 1,2,4 Of the various injury producing properties of lightning, the most likely to be implicated in the pathogenesis of these lesions, is the cylindrical shock-wave which expands from the lightning bolt. The tympanic membrane in close proximity to the lightning bolt is suddenly stressed with enough force to cause it to rupture. s In addition to acoustic trauma, lightning involves an energy discharge of approximately 100kW and part of this may also be transmitted to the inner ear. These effects can occur either when the lightning strikes the person directly or indirectly. The effect oflightning on the audio vestibular apparatus varies with the existing conditions when lightning strikes, such as, the duration of the shock sustained, the anatomical contact point of the bolt, and the impedance of the path through the body.s The current flow seeks the lowest impedance pathway, therefore, the impedances of various tissues through or over which current may pass will determine its course. The average bolt carries 10,000 to 20,000 amperes and has a duration of 3 msec. The impact with which this sonic shock wave strikes the tympanic membrane varies directly with the distance of the body from the axis of the lightning bolt. 6 Thus, lightning may affect the ear in two ways: rupture of a tympanic membrane, which is almost always the case, and occasionally a sensorineural hearing loss. The perforation may be unilateral, whereas the sensorineural hearing loss can be bilateral. The sensorineural hearing loss may be transient or for a longer period, and none so far has been reported as permanent. S According to us, labyrinthine membrane rupture may occur leading to unilateral or bilateral sensorineural hearing loss. The cases of sensorineural hearing loss due to lightning induced trauma show multiple haemorrhages and edema in the inner ear. An interesting possibility as stated by Boyes, is that histamine produced by trauma causes local vasodilation and fluid exudation due to increased permeability. This leads to pressure on the fibers of the cochlear nerve resulting in degeneration and deafness. However, if the vascular tone recovers, the function of the nerve may recover partially or completely. This would explain the rapid and complete recovery of hearing in some cases and the partial recovery in others. 7 Experiments undertaken by the Jutland Telephone Co. show that lightning with transmission through the telephone network may cause a sound pressure of 15O-160dB SPL which is enough to cause rupture of the tympanic membrane in persons with weak tympanic membrane. s Kristensen and Tveteras (1985) have reported a unique case in which two persons simultaneously sustained rupture of the tympanic membrane by lightning conducted through the telephone cable.

ACOUSTIC EFFECTS OF LIGHTNING

289

CONCLUSION

We have experienced 2 cases of cochlear injury due to lightning, one in which the audio vestibular apparatus was struck directly, resulting in unilateral tympanic membrane perforation and conductive hearing loss, and in the other indirect trauma resulted in mixed hearing loss. We thank the Dean, Dr. K.D. Nihalani, B.Y.L. Nair Hospital and T.N. Medical College, for permitting us to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.

Bergstrom L, Neblett LM, Sando I, et al: The lightning damaged ear. Arch Otolaryngol 100:117121, 1974. Weiss KS: Otologic lightning bolts. Am J Otol 1:334-337, 1980. Arden CP, Harrison SH, Lister J, et al: Lightning accident at ascot. Br Med J 1:1450-1453, 1956. Drechsler B: Akustisk Trommehinderuptur ved Iynnedslag Ugeskrift for Laeger. 143:1535, 1981. Wright JW, Silk KL: Acoustic and vestibular defects in lightning survivors. Laryngoscope 84: 1378-1386, 1974. Kristensen S, Tveteras K: Lightning induced acoustic rupture of the tympanic membrane (A Report of two cases). J Laryngol Otol 99:711-713, 1985. Boyes Korkis F: Effect of blast on the human ear. Br Med J 1:198-201, 1946. Poulsen P, Knudstrup P: Lightning causing inner ear damage and intracranial haematoma. J LaryngolOtol 100:1067-1070, 1986.

Request reprints to:

Dr. U.K. Soni, Department of Otolaryngology, B.Y.L. Nair Hospital, Bombay-400 008, India