Unilateral Sensorineural Hearing Loss in Adults: Etiology and Management

ABSTRACT

Unilateral sensorineural hearing loss (SNHL) affects people at any age, can present as an acute and/or progressive process, and can range from mild to profound. Although the great majority of cases have an unknown cause, the known causes of unilateral SNHL need to be excluded including neoplasms, stroke, demyelinating and autoimmune diseases, infection, perilymphatic fistula, and Ménière's disease. The majority of individuals with idiopathic sudden SNHL will recover complete or partial hearing. However, there is a small subset of patients who remain with unilateral hearing impairment, which can result in communication difficulties. The goal of this article is to present the etiology and medical management of unilateral SNHL in the adult population.

KEYWORDS

Baha (bone-anchored hearing aid) - CROS (contralateral routing of the signal) - single-sided deafness - unilateral sensorineural hearing loss

REFERENCES

• 1 Agrawal Y, Platz E A, Niparko J K. Prevalence of hearing loss and differences by demographic characteristics among US adults: data from the National Health and Nutrition Examination Survey, 1999–2004.  Arch Intern Med. 2008;  168(14) 1522-1530
• 2 Popelka G R, Derebery J, Blevins N H et al. Preliminary evaluation of a novel bone-conduction device for single-sided deafness.  Otol Neurotol. 2010;  31(3) 492-497
• 3 Baguley D M, Bird J, Humphriss R L, Prevost A T. The evidence base for the application of contralateral bone anchored hearing aids in acquired unilateral sensorineural hearing loss in adults.  Clin Otolaryngol. 2006;  31(1) 6-14
• 4 Newman C W, Sandridge S A, Wodzisz L M. Longitudinal benefit from and satisfaction with the Baha system for patients with acquired unilateral sensorineural hearing loss.  Otol Neurotol. 2008;  29(8) 1123-1131
• 5 Welsh L W, Welsh J J, Rosen L F, Dragonette J E. Functional impairments due to unilateral deafness.  Ann Otol Rhinol Laryngol. 2004;  113(12) 987-993
• 6 Chiossoine-Kerdel J A, Baguley D M, Stoddart R L, Moffat D A. An investigation of the audiologic handicap associated with unilateral sudden sensorineural hearing loss.  Am J Otol. 2000;  21(5) 645-651
• 7 Newman C W, Jacobson G P, Hug G A, Sandridge S A. Perceived hearing handicap of patients with unilateral or mild hearing loss.  Ann Otol Rhinol Laryngol. 1997;  106(3) 210-214
• 8 Newman C W, Weinstein B E, Jacobson G P, Hug G A. The Hearing Handicap Inventory for Adults: psychometric adequacy and audiometric correlates.  Ear Hear. 1990;  11(6) 430-433
• 9 Hughes G B, Freedman M A, Haberkamp T J, Guay M E. Sudden sensorineural hearing loss.  Otolaryngol Clin North Am. 1996;  29(3) 393-405
• 10 Byl Jr F M. Sudden hearing loss: eight years' experience and suggested prognostic table.  Laryngoscope. 1984;  94(5 Pt 1) 647-661
• 11 Shaia F T, Sheehy J L. Sudden sensori-neural hearing impairment: a report of 1,220 cases.  Laryngoscope. 1976;  86(3) 389-398
• 12 Mattox D E, Simmons F B. Natural history of sudden sensorineural hearing loss.  Ann Otol Rhinol Laryngol. 1977;  86(4 Pt 1) 463-480
• 13 Fetterman B L, Saunders J E, Luxford W M. Prognosis and treatment of sudden sensorineural hearing loss.  Am J Otol. 1996;  17(4) 529-536
• 14 Megighian D, Bolzan M, Barion U, Nicolai P. Epidemiological considerations in sudden hearing loss: a study of 183 cases.  Arch Otorhinolaryngol. 1986;  243(4) 250-253
• 15 Alexiou C, Arnold W, Fauser C et al. Sudden sensorineural hearing loss: does application of glucocorticoids make sense?.  Arch Otolaryngol Head Neck Surg. 2001;  127(3) 253-258
• 16 Kallinen J, Laurikainen E, Laippala P, Grénman R. Sudden deafness: a comparison of anticoagulant therapy and carbogen inhalation therapy.  Ann Otol Rhinol Laryngol. 1997;  106(1) 22-26
• 17 Nakashima T, Itoh A, Misawa H, Ohno Y. Clinicoepidemiologic features of sudden deafness diagnosed and treated at university hospitals in Japan.  Otolaryngol Head Neck Surg. 2000;  123(5) 593-597
• 18 Yanagita N, Nakashima T, Ohno Y, Kanzaki J, Shitara T. Estimated annual number of patients treated for sensorineural hearing loss in Japan. Results of a nationwide epidemiological survey in 1987.  Acta Otolaryngol Suppl. 1994;  514 9-13
• 19 Minoda R, Masuyama K, Habu K, Yumoto E. Initial steroid hormone dose in the treatment of idiopathic sudden deafness.  Am J Otol. 2000;  21(6) 819-825
• 20 Rauch S D. Clinical practice. Idiopathic sudden sensorineural hearing loss.  N Engl J Med. 2008;  359(8) 833-840
• 21 Grandis J R, Hirsch B E, Wagener M M. Treatment of idiopathic sudden sensorineural hearing loss.  Am J Otol. 1993;  14(2) 183-185
• 22 Wilkins Jr S A, Mattox D E, Lyles A. Evaluation of a “shotgun” regimen for sudden hearing loss.  Otolaryngol Head Neck Surg. 1987;  97(5) 474-480
• 23 Wilson W R, Laird N, Moo-Young G, Soeldner J S, Kavesh D A, MacMeel J W. The relationship of idiopathic sudden hearing loss to diabetes mellitus.  Laryngoscope. 1982;  92(2) 155-160
• 24 Wilson W R, Byl F M, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. A double-blind clinical study.  Arch Otolaryngol. 1980;  106(12) 772-776
• 25 Jaffee B F. Sudden deafness. An otologic emergency.  Arch Otolaryngol. 1967;  86(1) 55-60
• 26 Schick B, Brors D, Koch O, Schäfers M, Kahle G. Magnetic resonance imaging in patients with sudden hearing loss, tinnitus and vertigo.  Otol Neurotol. 2001;  22(6) 808-812
• 27 Fitzgerald D C, Mark A S. Sudden hearing loss: frequency of abnormal findings on contrast-enhanced MR studies.  AJNR Am J Neuroradiol. 1998;  19(8) 1433-1436
• 28 Aarnisalo A A, Suoranta H, Ylikoski J. Magnetic resonance imaging findings in the auditory pathway of patients with sudden deafness.  Otol Neurotol. 2004;  25(3) 245-249
• 29 Shinohara S, Yamamoto E, Saiwai S et al. Clinical features of sudden hearing loss associated with a high signal in the labyrinth on unenhanced T1-weighted magnetic resonance imaging.  Eur Arch Otorhinolaryngol. 2000;  257(9) 480-484
• 30 Saunders J E, Luxford W M, Devgan K K, Fetterman B L. Sudden hearing loss in acoustic neuroma patients.  Otolaryngol Head Neck Surg. 1995;  113(1) 23-31
• 31 Arts H A. Sensorineural hearing loss: evaluation and management in adults. In: Cummings CW Cummings: Otolaryngology Head and Neck Surgery. 4th ed. Philadelphia, PA; Mosby 2005: 3535-3555
• 32 Zulch K J. Epidemiology of brain tumors: general statistical and biological data. In: Zulch KJ Brain Tumors: Their Biology and Pathology. 3rd ed. Berlin, Germany; Springer-Verlag 1986: 85-112
• 33 Moffat D A, Baguley D M, von Blumenthal H, Irving R M, Hardy D G. Sudden deafness in vestibular schwannoma.  J Laryngol Otol. 1994;  108(2) 116-119
• 34 Selesnick S H, Jackler R K, Pitts L W. The changing clinical presentation of acoustic tumors in the MRI era.  Laryngoscope. 1993;  103(4 Pt 1) 431-436
• 35 Higgs W A. Sudden deafness as the presenting symptom of acoustic neurinoma.  Arch Otolaryngol. 1973;  98(2) 73-76
• 36 Fahy C, Nikolopoulos T P, O'Donoghue G M. Acoustic neuroma surgery and tinnitus.  Eur Arch Otorhinolaryngol. 2002;  259(6) 299-301
• 37 Hoistad D L, Melnik G, Mamikoglu B, Battista R, O'Connor C A, Wiet R J. Update on conservative management of acoustic neuroma.  Otol Neurotol. 2001;  22(5) 682-685
• 38 Tos M, Stangerup S E, Cayé-Thomasen P, Tos T, Thomsen J. What is the real incidence of vestibular schwannoma?.  Arch Otolaryngol Head Neck Surg. 2004;  130(2) 216-220
• 39 Charabi S, Tos M, Thomsen J, Charabi B, Mantoni M. Vestibular schwannoma growth—long-term results.  Acta Otolaryngol Suppl. 2000;  543 7-10
• 40 Friedman R A, Kesser B, Brackmann D E, Fisher L M, Slattery W H, Hitselberger W E. Long-term hearing preservation after middle fossa removal of vestibular schwannoma.  Otolaryngol Head Neck Surg. 2003;  129(6) 660-665
• 41 Shen T, Friedman R A, Brackmann D E et al. The evolution of surgical approaches for posterior fossa meningiomas.  Otol Neurotol. 2004;  25(3) 394-397
• 42 Paz-Fumagalli R, Daniels D L, Millen S J, Meyer G A, Thieu T M. Dural “tail” associated with an acoustic schwannoma in MR imaging with gadopentetate dimeglumine.  AJNR Am J Neuroradiol. 1991;  12(6) 1206
• 43 Wiet R J, Mamikoglu B, Odom L, Hoistad D L. Long-term results of the first 500 cases of acoustic neuroma surgery.  Otolaryngol Head Neck Surg. 2001;  124(6) 645-651
• 44 Kemink J L, LaRouere M J, Kileny P R, Telian S A, Hoff J T. Hearing preservation following suboccipital removal of acoustic neuromas.  Laryngoscope. 1990;  100(6) 597-602
• 45 Baldwin D L, King T T, Morrison A W. Hearing conservation in acoustic neuroma surgery via the posterior fossa.  J Laryngol Otol. 1990;  104(6) 463-467
• 46 Fischer G, Fischer C, Rémond J. Hearing preservation in acoustic neurinoma surgery.  J Neurosurg. 1992;  76(6) 910-917
• 47 Norén G, Greitz D, Hirsch A, Lax I. Gamma knife surgery in acoustic tumours.  Acta Neurochir Suppl (Wien). 1993;  58 104-107
• 48 Hirsch A, Norén G, Anderson H. Audiologic findings after stereotactic radiosurgery in nine cases of acoustic neurinomas.  Acta Otolaryngol. 1979;  88(3-4) 155-160
• 49 Lunsford L D, Linskey M E. Stereotactic radiosurgery in the treatment of patients with acoustic tumors.  Otolaryngol Clin North Am. 1992;  25(2) 471-491
• 50 Foote R L, Coffey R J, Swanson J W et al. Stereotactic radiosurgery using the gamma knife for acoustic neuromas.  Int J Radiat Oncol Biol Phys. 1995;  32(4) 1153-1160
• 51 Flickinger J C, Kondziolka D, Niranjan A, Lunsford L D. Results of acoustic neuroma radiosurgery: an analysis of 5 years' experience using current methods.  J Neurosurg. 2001;  94(1) 1-6
• 52 Roland P S, Eston D. Stereotactic radiosurgery of acoustic tumors.  Otolaryngol Clin North Am. 2002;  35(2) 343-355
• 53 Schuknecht H F. Pathology of the Ear. 2nd ed. Philadelphia, PA; Lea and Febiger 1993
• 54 Noffsinger D, Olsen W O, Carhart R, Hart C W, Sahgal V. Auditory and vestibular aberrations in multiple sclerosis.  Acta Otolaryngol Suppl. 1972;  303 1-63
• 55 Grénman R. Involvement of the audiovestibular system in multiple sclerosis. An otoneurologic and audiologic study.  Acta Otolaryngol Suppl. 1985;  420 1-95
• 56 Franklin D J, Coker N J, Jenkins H A. Sudden sensorineural hearing loss as a presentation of multiple sclerosis.  Arch Otolaryngol Head Neck Surg. 1989;  115(1) 41-45
• 57 Drulović B, Ribarić-Jankes K, Kostić V, Sternić N. Multiple sclerosis as the cause of sudden “pontine” deafness.  Audiology. 1994;  33(4) 195-201
• 58 Daugherty W T, Lederman R J, Nodar R H, Conomy J P. Hearing loss in multiple sclerosis.  Arch Neurol. 1983;  40(1) 33-35
• 59 Hopf H C, Maurer K. Wave I of early auditory evoked potentials in multiple sclerosis.  Electroencephalogr Clin Neurophysiol. 1983;  56(1) 31-37
• 60 Keith R W, Garza-Holquin Y, Smolak L, Pensak M L. Acoustic reflex dynamics and auditory brain stem responses in multiple sclerosis.  Am J Otol. 1987;  8(5) 406-413
• 61 Musiek F E, Gollegly K M, Kibbe K S, Reeves A G. Electrophysiologic and behavioral auditory findings in multiple sclerosis.  Am J Otol. 1989;  10(5) 343-350
• 62 Schweitzer V G, Shepard N. Sudden hearing loss: an uncommon manifestation of multiple sclerosis.  Otolaryngol Head Neck Surg. 1989;  100(4) 327-332
• 63 Verma N P, Lynn G E. Auditory evoked responses in multiple sclerosis. Wave I abnormality.  Arch Otolaryngol. 1985;  111(1) 22-24
• 64 Armington W G, Harnsberger H R, Smoker W R, Osborn A G. Normal and diseased acoustic pathway: evaluation with MR imaging.  Radiology. 1988;  167(2) 509-515
• 65 Curé J K, Cromwell L D, Case J L, Johnson G D, Musiek F E. Auditory dysfunction caused by multiple sclerosis: detection with MR imaging.  AJNR Am J Neuroradiol. 1990;  11(4) 817-820
• 66 Drulović B, Ribarić-Jankes K, Kostić V S, Sternić N. Sudden hearing loss as the initial monosymptom of multiple sclerosis.  Neurology. 1993;  43(12) 2703-2705
• 67 Gebarski S S, Gabrielsen T O, Gilman S, Knake J E, Latack J T, Aisen A M. The initial diagnosis of multiple sclerosis: clinical impact of magnetic resonance imaging.  Ann Neurol. 1985;  17(5) 469-474
• 68 Wells M, Michaels L, Wells D G. Otolaryngological disturbances in Waldenstrom's macroglobulinaemia.  Clin Otolaryngol Allied Sci. 1977;  2(4) 327-338
• 69 Nomura Y, Tsuchida M, Mori S, Sakurai T. Deafness in cryoglobulinemia.  Ann Otol Rhinol Laryngol. 1982;  91(3 Pt 1) 250-255
• 70 Hotaling A J, Hillstrom R P, Bazell C. Sickle cell crisis and sensorineural hearing loss: case report and discussion.  Int J Pediatr Otorhinolaryngol. 1989;  17(3) 207-211
• 71 O'Keeffe L J, Maw A R. Sudden total deafness in sickle cell disease.  J Laryngol Otol. 1991;  105(8) 653-655
• 72 Tavin M E, Rubin J S, Camacho F J. Sudden sensorineural hearing loss in haemoglobin SC disease.  J Laryngol Otol. 1993;  107(9) 831-833
• 73 Crook J P. Congenital fistula in the stapedial footplate.  South Med J. 1967;  60(11) 1168-1170
• 74 Guindi G M. Congenital labyrintho-tympanic fistula—a recently recognized entity in children.  J Otolaryngol. 1981;  10(1) 67-71
• 75 Adkisson G H, Meredith A P. Inner ear decompression sickness combined with a fistula of the round window. Case report.  Ann Otol Rhinol Laryngol. 1990;  99(9 Pt 1) 733-737
• 76 Pullen II F W, Rosenberg G J, Cabeza C H. Sudden hearing loss in divers and fliers.  Laryngoscope. 1979;  89(9 Pt 1) 1373-1377
• 77 Black F O, Pesznecker S, Norton T et al. Surgical management of perilymphatic fistulas: a Portland experience.  Am J Otol. 1992;  13(3) 254-262
• 78 Davis R E. Diagnosis and management of perilymph fistula: the University of North Carolina approach.  Am J Otol. 1992;  13(1) 85-89
• 79 Calhoun K H, Strunk C L. Perilymph fistula.  Arch Otolaryngol Head Neck Surg. 1992;  118(7) 693-694
• 80 Sande M A, Mandell G L. Antimicrobial agents. In: Gilman AG, Goodman LS, Gilman A The Pharmacological Basis of Therapeutics. New York, NY; Macmillan 1980: 1080-1222
• 81 Dolan S, Everett E D, Renner L. Hearing loss in Rocky Mountain spotted fever.  Ann Intern Med. 1986;  104(2) 285
• 82 Steinfeld H J, Silverstein J, Weisburger W, Rattner. Deafness associated with Rocky Mountain spotted fever.  Md Med J. 1988;  37(4) 287-288
• 83 Hanner P, Rosenhall U, Edström S, Kaijser B. Hearing impairment in patients with antibody production against Borrelia burgdorferi antigen.  Lancet. 1989;  1(8628) 13-15
• 84 Hallberg O E. Sudden deafness of obscure origin.  Laryngoscope. 1956;  66(10) 1237-1267
• 85 Berrocal J R, Ramírez-Camacho R. Sudden sensorineural hearing loss: supporting the immunologic theory.  Ann Otol Rhinol Laryngol. 2002;  111(11) 989-997
• 86 McCabe B F. Autoimmune sensorineural hearing loss.  Ann Otol Rhinol Laryngol. 1979;  88(5 Pt 1) 585-589
• 87 Harris J P. Autoimmunity of the inner ear.  Am J Otol. 1989;  10(3) 193-195
• 88 Harris J P, Sharp P A. Inner ear autoantibodies in patients with rapidly progressive sensorineural hearing loss.  Laryngoscope. 1990;  100(5) 516-524
• 89 Hughes G B, Kinney S E, Barna B P, Calabrese L H. Practical versus theoretical management of autoimmune inner ear disease.  Laryngoscope. 1984;  94(6) 758-767
• 90 Moscicki R A, San Martin J E, Quintero C H, Rauch S D, Nadol Jr J B, Bloch K J. Serum antibody to inner ear proteins in patients with progressive hearing loss. Correlation with disease activity and response to corticosteroid treatment.  JAMA. 1994;  272(8) 611-616
• 91 Mattox D E, Lyles C A. Idiopathic sudden sensorineural hearing loss.  Am J Otol. 1989;  10(3) 242-247
• 92 Van Dishoeck H A, Bierman T A. Sudden perceptive deafness and viral infection; report of the first one hundred patients.  Ann Otol Rhinol Laryngol. 1957;  66(4) 963-980
• 93 Wilson W R. The relationship of the herpesvirus family to sudden hearing loss: a prospective clinical study and literature review.  Laryngoscope. 1986;  96(8) 870-877
• 94 Khetarpal U, Nadol Jr J B, Glynn R J. Idiopathic sudden sensorineural hearing loss and postnatal viral labyrinthitis: a statistical comparison of temporal bone findings.  Ann Otol Rhinol Laryngol. 1990;  99(12) 969-976
• 95 Vasama J P, Linthicum Jr F H. Idiopathic sudden sensorineural hearing loss: temporal bone histopathologic study.  Ann Otol Rhinol Laryngol. 2000;  109(6) 527-532
• 96 Yoon T H, Paparella M M, Schachern P A, Alleva M. Histopathology of sudden hearing loss.  Laryngoscope. 1990;  100(7) 707-715
• 97 Schuknecht H F, Donovan E D. The pathology of idiopathic sudden sensorineural hearing loss.  Arch Otorhinolaryngol. 1986;  243(1) 1-15
• 98 Perlman H B, Kimura R, Fernandez C. Experiments on temporary obstruction of the internal auditory artery.  Laryngoscope. 1959;  69(6) 591-613
• 99 Simmons F B. Theory of membrane breaks in sudden hearing loss.  Arch Otolaryngol. 1968;  88(1) 41-48
• 100 Gussen R. Sudden hearing loss associated with cochlear membrane rupture. Two human temporal bone reports.  Arch Otolaryngol. 1981;  107(10) 598-600
• 101 Merchant S N, Adams J C, Nadol Jr J B. Pathology and pathophysiology of idiopathic sudden sensorineural hearing loss.  Otol Neurotol. 2005;  26(2) 151-160
• 102 Chen C Y, Halpin C, Rauch S D. Oral steroid treatment of sudden sensorineural hearing loss: a ten year retrospective analysis.  Otol Neurotol. 2003;  24(5) 728-733
• 103 Moskowitz D, Lee K J, Smith H W. Steroid use in idiopathic sudden sensorineural hearing loss.  Laryngoscope. 1984;  94(5 Pt 1) 664-666
• 104 Parnes L S, Sun A H, Freeman D J. Corticosteroid pharmacokinetics in the inner ear fluids: an animal study followed by clinical application.  Laryngoscope. 1999;  109(7 Pt 2) 1-17
• 105 Lefebvre P P, Staecker H. Steroid perfusion of the inner ear for sudden sensorineural hearing loss after failure of conventional therapy: a pilot study.  Acta Otolaryngol. 2002;  122(7) 698-702
• 106 Gianoli G J, Li J C. Transtympanic steroids for treatment of sudden hearing loss.  Otolaryngol Head Neck Surg. 2001;  125(3) 142-146
• 107 Banerjee A, Parnes L S. Intratympanic corticosteroids for sudden idiopathic sensorineural hearing loss.  Otol Neurotol. 2005;  26(5) 878-881
• 108 Fitzgerald D C, McGuire J F. Intratympanic steroids for idiopathic sudden sensorineural hearing loss.  Ann Otol Rhinol Laryngol. 2007;  116(4) 253-256
• 109 Haynes D S, O'Malley M, Cohen S, Watford K, Labadie R F. Intratympanic dexamethasone for sudden sensorineural hearing loss after failure of systemic therapy.  Laryngoscope. 2007;  117(1) 3-15
• 110 Slattery W H, Fisher L M, Iqbal Z, Friedman R A, Liu N. Intratympanic steroid injection for treatment of idiopathic sudden hearing loss.  Otolaryngol Head Neck Surg. 2005;  133(2) 251-259
• 111 Battaglia A, Burchette R, Cueva R. Combination therapy (intratympanic dexamethasone + high-dose prednisone taper) for the treatment of idiopathic sudden sensorineural hearing loss.  Otol Neurotol. 2008;  29(4) 453-460
• 112 Lautermann J, Sudhoff H, Junker R. Transtympanic corticoid therapy for acute profound hearing loss.  Eur Arch Otorhinolaryngol. 2005;  262(7) 587-591
• 113 Stokroos R J, Albers F W, Tenvergert E M. Antiviral treatment of idiopathic sudden sensorineural hearing loss: a prospective, randomized, double-blind clinical trial.  Acta Otolaryngol. 1998;  118(4) 488-495
• 114 Tucci D L, Farmer Jr J C, Kitch R D, Witsell D L. Treatment of sudden sensorineural hearing loss with systemic steroids and valacyclovir.  Otol Neurotol. 2002;  23(3) 301-308
• 115 Westerlaken B O, de Kleine E, van der Laan B, Albers F. The treatment of idiopathic sudden sensorineural hearing loss using pulse therapy: a prospective, randomized, double-blind clinical trial.  Laryngoscope. 2007;  117(4) 684-690
• 116 Van de Heyning P, Vermeire K, Diebl M, Nopp P, Anderson I, De Ridder D. Incapacitating unilateral tinnitus in single-sided deafness treated by cochlear implantation.  Ann Otol Rhinol Laryngol. 2008;  117(9) 645-652
• 117 Vermeire K, Van de Heyning P. Binaural hearing after cochlear implantation in subjects with unilateral sensorineural deafness and tinnitus.  Audiol Neurootol. 2009;  14(3) 163-171

APPENDIX A

• Embolism: Occlusion of a blood vessel by an embolus an abnormal particle (i.e., blood clot or air bubble) that circulates in the blood.

• Horner's syndrome: Damage to the cervical sympathetic trunk causing a constellation of symptoms including ptosis (drooping eyelid), miosis (small pupil), and anhidrosis (decreased sweating on the affected side of the face).

• Idiopathic: Arising from an unknown cause.

• Meningogenic: Of or originating from the meninges (three membranes that cover the brain and spinal cord).

• Otogenic: Of or originating within the ear.

• Parenteral: Drug administration by means other than through the alimentary tract (as by intramuscular or intravenous injection).

• Seroconversion: The development of detectable antibodies in the blood directed against an infectious agent.

• Serous: Pertaining to serum; thin and watery.

• Suppurative: Relating to suppuration—pus: a fluid product of inflammation.

• Thrombosis: The formation or presence of a thrombus (a clot of coagulated blood attached at the site of its formation) in a blood vessel.

• Titer: Concentration of a substance in solution or the strength of such a substance determined by titration.