What are the causes and treatment options for a condition of unilateral etiology?

Causes of Unilateral Etiology

Otologic Causes

Unilateral hearing loss requires immediate evaluation to distinguish between conductive and sensorineural etiologies, as the underlying causes and urgency of management differ significantly. 1

Sudden Sensorineural Hearing Loss (SSNHL)

• Most cases of SSNHL are idiopathic and unilateral, requiring urgent evaluation and corticosteroid therapy within 2 weeks of onset for optimal outcomes. 2
• Rare causes of unilateral SNHL include auditory neuropathy, chemoradiotherapy effects, dialysis-induced hearing loss, common cavity inner ear malformation, multiple sclerosis, acute otitis media complications, and vertebrobasilar dolichoectasia. 3
• Vestibular schwannoma (acoustic neuroma) commonly presents with unilateral tinnitus and progressive hearing loss, necessitating MRI with contrast to exclude retrocochlear pathology. 2

Conductive Hearing Loss

• Weber test lateralizing to one ear indicates either conductive hearing loss in that ear OR sensorineural hearing loss in the opposite ear. 1
• Unilateral conductive causes include cerumen impaction, middle ear effusion, tympanic membrane perforation, cholesteatoma, or vascular retrotympanic masses (glomus tumors, aberrant internal carotid artery, dehiscent jugular bulb). 2

Meniere Disease

• Meniere disease typically begins unilaterally but progresses to bilateral involvement in a subset of patients. 1
• Patients with bilateral Meniere disease present at a significantly younger age and have higher incidence of personal migraine history and family history of Meniere disease compared to unilateral cases. 4
• Antecedent fluctuating hearing loss on one or both sides, particularly with isolated low-frequency hearing trough, suggests Meniere disease. 1

Neurologic Causes

Trigeminal Nerve Pathology

• Unilateral facial numbness and tingling without rash or pain requires MRI brain with contrast as the essential first-line imaging to evaluate the trigeminal nerve pathway from brainstem to peripheral branches. 5
• This presentation indicates trigeminal neuropathy rather than classical trigeminal neuralgia, which manifests as paroxysmal electric shock-like pain with mandatory refractory periods, not continuous sensory symptoms. 5
• Progressive or persistent symptoms beyond 2-4 months warrant imaging even if initially attributed to benign causes. 5

Glossopharyngeal Neuralgia and Referred Otalgia

• Unilateral ear pain with neurologic symptoms (weakness, dysarthria, ataxia, facial numbness) suggests central nervous system pathology, particularly brainstem involvement, requiring immediate neuroimaging. 6
• Stroke or TIA should be considered when ear pain occurs with arm tingling and scalp paresthesias, especially involving the lateral pontomedullary region. 6
• Glossopharyngeal neuralgia presents with sharp, shooting pain triggered by swallowing, requiring first-line treatment with anticonvulsants (carbamazepine or oxcarbazepine). 6

Peripheral Neuropathy

• Unilateral peripheral neuropathy respecting the midline is extremely rare and may represent a mosaic or chimeric form of Charcot-Marie-Tooth disease, though genetic testing from blood may be negative. 7
• This phenotype typically presents with onset in early childhood, slowly progressive course, and absence of family history or structural CNS lesions. 7

Vascular Causes

Renovascular Disease

• Unilateral renal artery stenosis with normal renal function is typically treated with percutaneous balloon angioplasty and stenting rather than surgical intervention. 1
• Fibromuscular dysplasia causing renovascular hypertension should be treated with percutaneous transluminal renal angioplasty (PTRA) without stenting as first-line therapy. 1
• Unilateral atherosclerotic renal artery stenosis can be managed medically with renin-angiotensin system blockade and periodic surveillance when the contralateral kidney is normal. 1

Respiratory Causes

Interstitial Lung Abnormalities

• Although ILAs are defined as bilateral parenchymal abnormalities, patients with strong family history or known genetic variants who have unilateral findings may be at risk of future progression to interstitial lung disease. 1
• Patients with connective tissue disease or occupational exposures may present with unilateral abnormalities, though data on progression risk is limited and findings often represent non-ILA etiologies. 1

Pleural Disease

Unilateral Pleural Effusion

• Unilateral pleural effusion requires thoracentesis with at least 25-50 mL sent for cytological examination to distinguish between malignant, inflammatory, infectious, and cardiovascular causes. 1
• Secondary pleural malignancy is diagnosed by malignant fluid cytology, pleural biopsy, or malignant pleural nodules/thickening on imaging with confirmed extrapleural primary cancer. 1
• Tuberculous pleural effusion should be suspected with granulomatous histology or lymphocytic fluid, particularly when effusion resolves after TB therapy. 1

Endocrine Causes

Primary Aldosteronism

• Primary aldosteronism may present with unilateral adrenal lesions amenable to surgical removal, distinguished from bilateral disease by adrenal vein sampling or functional imaging with radiolabelled tracers. 1
• Unilateral primary aldosteronism in younger patients without significant comorbidities should be treated with surgical removal of the affected adrenal gland. 1

Otitis Media with Effusion

Chronic OME

• Chronic unilateral OME for 3 months or longer with symptoms attributable to OME (balance problems, poor school performance, behavioral problems, ear discomfort, reduced quality of life) warrants consideration of tympanostomy tube insertion. 1
• Children with chronic OME demonstrate significantly poorer vestibular function and gross motor proficiency compared to non-OME controls, with deficiencies resolving promptly following tympanostomy tube insertion. 1

Critical Red Flags Requiring Urgent Evaluation

• Sudden onset of bilateral hearing loss, concurrent severe bilateral vestibular loss with oscillopsia, accompanying focal weakness, dysarthria, hemiataxia, encephalopathy, severe headaches, or diplopia suggest systemic disorders requiring immediate comprehensive evaluation. 1
• Downbeating or gaze-evoked nystagmus with hearing loss warrants brain imaging to exclude stroke or structural lesions. 1
• Severe head trauma or recent acoustic trauma coincident with hearing loss requires temporal bone imaging. 1
• History of concurrent or recent eye pain, redness, lacrimation, and photophobia with hearing loss suggests autoimmune inner ear disease or Cogan syndrome. 1