What are the causes of dryness of the oral mucosa (xerostomia) in patients, particularly older adults or those with medical conditions such as Sjögren's syndrome, diabetes, or Parkinson's disease?

Causes of Oral Mucosal Dryness (Xerostomia)

Medications are the most common cause of xerostomia in clinical practice, particularly in older adults who are frequently on multiple drugs, with anticholinergic agents being the primary culprits. 1, 2, 3

Medication-Induced Causes

Anticholinergic Medications

• Centrally acting anticholinergics (scopolamine, atropine) directly block muscarinic receptors, causing dry mouth along with systemic anticholinergic effects 1
• Tricyclic antidepressants have significant anticholinergic properties and are common xerostomia causes 1
• Cyclobenzaprine produces dry mouth as one of its most frequent adverse reactions through anticholinergic mechanisms 1
• Antihistamines contribute to reduced saliva flow through anticholinergic pathways 1, 2

Cardiovascular Medications

• Beta-blockers (atenolol, metoprolol, propranolol) cause dry mouth through anti-adrenergic effects, with atenolol producing more pronounced effects than propranolol 1, 2
• Centrally acting antihypertensives like clonidine cause dry mouth as one of their most prevalent adverse effects through alpha-adrenergic mechanisms 1, 2

Psychotropic Medications

• SSRIs, particularly fluoxetine, cause dry mouth with higher doses associated with greater frequency and severity 1, 2
• Bupropion commonly causes dry mouth as a side effect 1, 2

Other Medication Classes

• Opioids commonly cause dry mouth as an adverse effect 1, 2
• Stimulant medications (phentermine, lisdexamfetamine) cause dry mouth in a significant percentage of users 1, 2
• Anti-obesity medications (phentermine/topiramate, naltrexone/bupropion) list dry mouth as a common side effect 1, 2
• Analgesics, antipyretics, antibiotics, and vaccines can all contribute to reduced saliva flow 1, 2

Polypharmacy Effect

• The anticholinergic burden of multiple medications substantially increases xerostomia risk, especially in older adults 1
• Elderly patients face substantially higher risk due to multiple medications combined with age-related decline in salivary flow 1, 2

Autoimmune and Systemic Disease Causes

Sjögren's Syndrome

• Sjögren's syndrome is characterized by lymphocytic infiltration of lacrimal and salivary glands, affecting approximately 0.4% of the population with a female-to-male ratio of 20:1 1, 2
• This represents a primary autoimmune cause of salivary gland dysfunction 4

Related Autoimmune Conditions

• Sicca syndrome presents with abrupt onset dry mouth, usually without dry eyes, and can occur independently of Sjögren's syndrome 1, 2
• Rheumatoid arthritis can cause salivary gland hypofunction 1, 2
• Primary biliary cholangitis (PBC) commonly presents with sicca complex symptoms of dry eyes and/or dry mouth 2

Metabolic and Systemic Diseases

• Diabetes mellitus is associated with dry mouth 2, 5
• Heart failure is associated with dry mouth 2
• Renal failure is associated with dry mouth 2
• Thyroid dysfunction can diminish salivation 5
• Nephritis can contribute to xerostomia 5

Age-Related Factors

• Salivary flow rate declines with age, making older adults more susceptible to dry mouth even without other risk factors 1, 2
• Aging results in lower salivary flow rates, which in combination with medication effects leads to xerostomia onset 4
• Saliva undergoes chemical changes with aging—ptyalin decreases while mucin increases, making saliva thick and viscous 5

Important caveat: Healthy aging preserves salivary gland function well, so dry mouth is probably not a condition of aging itself but most likely of systemic or extrinsic origin 5

Neurological Conditions

• Parkinson's disease is associated with swallowing disorders and contributes to xerostomia 4
• Dementia is associated with dysphagia and related oral symptoms 4
• Stroke commonly leads to oropharyngeal dysphagia and associated oral dryness 4

Additional Contributing Factors

Lifestyle and Environmental

• Chronic mouth breathing can dry the oral mucosa 5
• Dehydration from any cause worsens the perception and severity of xerostomia 2
• Fluid intake restrictions compound medication-induced dry mouth 2
• Alcohol and caffeine intake contribute to dry mouth 3

Medical Interventions

• Radiation therapy to the head and neck causes xerostomia 6, 7, 5
• Chemotherapy for cancer causes dry mouth 7
• Endotracheal intubation can result in dysphagia and oral dryness 4

Other Medical Conditions

• Autonomic dysfunction is strongly associated with dry mouth and can cause significant complications 2
• Obstructive sleep apnea with daytime somnolence is strongly associated with dry mouth symptoms 2
• Autoimmune diseases beyond Sjögren's can cause xerostomia 7
• Hormone disorders contribute to dry mouth 7
• Infections can cause dry mouth 7

Critical Diagnostic Pitfall

Always rule out conditions that mimic xerostomia: candidiasis, burning mouth syndrome, and dysphagia can present similarly to xerostomia but require different management 4, 1, 2

Paradoxical Exception

AChE inhibitors used for Alzheimer's disease actually increase saliva production, contrasting with most other medications that cause dry mouth 1, 2. This is an important exception to remember when reviewing medications in patients with dementia.