Essential Tremor: This is the most common cause of tremors, often presenting unilaterally and affecting the hands. The 5-month duration suggests a chronic condition, which aligns with essential tremor.

Parkinson's Disease: Although typically presenting with bilateral symptoms, Parkinson's disease can start unilaterally. The presence of a hand tremor, especially if accompanied by other symptoms like rigidity or bradykinesia, makes this a plausible diagnosis.
Dystonic Tremor: This condition can cause tremors, often in a specific part of the body, such as the hand. It might be considered if the tremor is associated with dystonic posturing or if it improves with sensory tricks.
Medication-induced Tremor: Certain medications can cause tremors as a side effect. Given the acute onset, if the patient has recently started a new medication, this could be a likely cause.

Multiple Sclerosis: Although less common, multiple sclerosis can present with a tremor, among other neurological symptoms. Missing this diagnosis could lead to delayed treatment and significant morbidity.
Stroke or Transient Ischemic Attack (TIA): A tremor could be a residual effect of a stroke or TIA, especially if there are other focal neurological deficits. Early recognition is crucial for secondary prevention.
Wilson's Disease: This rare genetic disorder can cause tremors, among other symptoms like liver disease and psychiatric issues. It's critical to diagnose early due to the availability of effective treatments that can prevent progression.

Neurodegenerative Disorders (e.g., Spinocerebellar Ataxias, Huntington's Disease): These conditions can present with tremors but are typically accompanied by other significant neurological symptoms.
Vitamin Deficiencies (e.g., Vitamin B12 Deficiency): Certain vitamin deficiencies can cause neurological symptoms, including tremors, but are less common causes.
Thyroid Disorders: Both hyperthyroidism and hypothyroidism can cause tremors, although they are usually bilateral and accompanied by other systemic symptoms.