Occupational Medicine · Supplementary · from Occupational Medicine

Case 2: Noise-Induced Hearing Loss

Patient Presentation

Demographics: 45-year-old male manufacturing plant press operator

Chief Complaint: "My wife says I'm turning the TV up too loud, and I've been having trouble hearing conversations at work — especially when there's background noise."

History of Present Illness: Mr. T.R. is referred to the occupational medicine clinic after his annual workplace audiometric screening revealed a significant bilateral high-frequency hearing loss, with a notable 15 dB threshold shift at 4000 Hz in the right ear compared to his baseline audiogram from 5 years ago. He has worked as a hydraulic press operator at an automotive stamping plant for 22 years. He reports that the noise level in his work area is consistently loud and that he can feel vibrations from the press through the floor.

He describes gradually progressive difficulty hearing conversations, particularly in noisy environments such as the plant floor, restaurants, and family gatherings. He frequently asks people to repeat themselves and has difficulty hearing his telephone unless the volume is at maximum. He also reports bilateral tinnitus — a constant high-pitched ringing that is worse in the right ear and more noticeable in quiet environments. The tinnitus has been present for approximately 5 years but has worsened over the past year.

He states he was provided foam earplugs from the beginning of employment but acknowledges inconsistent use during his first 10 years ("they were uncomfortable and I couldn't hear my coworkers"). He has been more compliant with hearing protection over the past 12 years, using both foam plugs and over-ear muffs. Despite this, noise exposure measurements at his workstation (performed by the company industrial hygienist 6 months ago) recorded 95-102 dBA TWA (time-weighted average), exceeding the OSHA Permissible Exposure Limit of 90 dBA.

Past Medical History:

• Type 2 diabetes mellitus (diagnosed 3 years ago, HbA1c 7.2%)
• Hyperlipidemia
• No history of ear infections, ear surgery, or head trauma
• No ototoxic medication use

Medications:

• Metformin 1000 mg BID
• Atorvastatin 20 mg daily

Social History:

• Non-smoker
• Recreational firearms use (deer hunting) for 20 years; inconsistent use of hearing protection while hunting
• Occasional power tool use at home (table saw, circular saw)
• No recreational headphone/earbud use with loud music
• Married, 2 children (ages 14 and 17)

Family History:

• Father: hearing aids at age 70 (attributed to aging)
• No family history of early-onset hearing loss

Physical Examination

• Vital Signs: BP 134/82 mmHg, HR 76 bpm, RR 14, SpO2 98%, Temp 36.7°C, BMI 31.2 kg/m²
• HEENT: External ears normal bilaterally; otoscopic examination reveals intact tympanic membranes bilaterally with normal landmarks, no effusion, no cerumen impaction
• Weber test: Lateralizes to the left ear (better hearing ear)
• Rinne test: Air conduction > bone conduction bilaterally (positive Rinne bilaterally, consistent with sensorineural hearing loss)
• Cranial nerves: Otherwise intact; no nystagmus; vestibular function grossly normal
• Neck: No lymphadenopathy, no masses

Workup and Results

Laboratory Studies:

Imaging/Additional Studies:

• Pure-tone audiometry: Bilateral sensorineural hearing loss (SNHL); characteristic 4-kHz "noise notch" with recovery at 8 kHz bilaterally; Right ear: 15 dB at 500 Hz, 20 dB at 1000 Hz, 25 dB at 2000 Hz, 55 dB at 3000 Hz, 65 dB at 4000 Hz, 50 dB at 6000 Hz, 35 dB at 8000 Hz; Left ear: 10 dB at 500 Hz, 15 dB at 1000 Hz, 20 dB at 2000 Hz, 45 dB at 3000 Hz, 55 dB at 4000 Hz, 45 dB at 6000 Hz, 30 dB at 8000 Hz
• Speech discrimination scores: Right ear 72%, Left ear 80% (reduced bilaterally)
• Tympanometry: Type A (normal) bilaterally; acoustic reflexes present but elevated bilaterally
• OSHA Standard Threshold Shift (STS) calculation: >10 dB average shift at 2000, 3000, and 4000 Hz in right ear compared to baseline — confirmed STS
• Workplace noise dosimetry (most recent): 98 dBA TWA at operator station; peak impulse levels 115 dBC during press strikes

Clinical Image

Audiogram illustrating the characteristic bilateral high-frequency sensorineural hearing loss with the classic 4-kHz "noise notch" and recovery at 8 kHz seen in noise-induced hearing loss. Source: Educational illustration.

Diagnosis

Bilateral Noise-Induced Hearing Loss (NIHL), Moderate Severity, Occupational

Key Diagnostic Criteria:

• Chronic occupational noise exposure exceeding OSHA PEL (98 dBA TWA vs. 90 dBA PEL)
• Bilateral sensorineural hearing loss with characteristic 4-kHz notch pattern
• OSHA Standard Threshold Shift confirmed (>10 dB average shift at 2000/3000/4000 Hz)
• Progressive decline documented on serial audiometric surveillance
• Consistent clinical history with gradual onset, bilateral involvement, and associated tinnitus
• No alternative etiology identified (no conductive component, no ototoxic medications, no acoustic neuroma suspected)
• Contributing factors: recreational noise exposure (firearms), diabetes mellitus (microvascular cochlear damage)

Treatment Plan

1. OSHA recordkeeping: Record STS on OSHA 300 Log as work-related hearing loss; notify employee in writing within 21 days
2. Enhanced hearing conservation:

• Fit-test for custom-molded earplugs with NRR ≥25 dB
• Dual protection (plugs + muffs) mandatory given exposures >100 dBA
• Engineering controls evaluation: press enclosure, vibration dampening, noise barriers
• Administrative controls: rotation to reduce cumulative daily exposure

1. Audiological rehabilitation:

• Referral to audiologist for hearing aid evaluation (bilateral)
• Assistive listening devices for workplace communication
• Aural rehabilitation program for communication strategies

1. Tinnitus management:

• Sound therapy (white noise generators/maskers)
• Cognitive behavioral therapy for tinnitus distress if significant
• Avoid silence (use ambient sound machines at night)

1. Medical optimization:

• Improve diabetes control (target HbA1c <7.0%) to reduce microvascular contribution
• Avoid ototoxic medications (aminoglycosides, high-dose aspirin, loop diuretics)

1. Recreational noise counseling: Mandatory hearing protection for firearms use; electronic shooting ear muffs recommended
2. Workers' compensation: File claim for occupational hearing loss; schedule impairment rating per AMA Guides (binaural hearing impairment calculation)
3. Follow-up audiometry: Every 6 months (increased frequency due to confirmed STS)

Key Learning Points

• Noise-induced hearing loss is the most common occupational disease in the United States and is entirely preventable; OSHA's Hearing Conservation Program (29 CFR 1910.95) mandates protection for workers exposed to ≥85 dBA TWA
• The characteristic audiometric pattern is a bilateral, roughly symmetric, sensorineural high-frequency loss with maximal deficit at 4000 Hz (the "4-kHz notch") and partial recovery at 8000 Hz, distinguishing it from presbycusis (age-related loss without notch)
• Standard Threshold Shift (STS) is defined as a ≥10 dB average change at 2000, 3000, and 4000 Hz in either ear compared to baseline; age correction is optional and controversial
• Diabetes mellitus is an independent risk factor for hearing loss via microvascular damage to the cochlear stria vascularis and is synergistic with noise exposure
• NIHL is irreversible because it results from permanent destruction of outer hair cells in the organ of Corti; the only treatment is hearing amplification and prevention of further damage

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