Benign nocturnal leg cramps: This condition is very common in the elderly, often occurring at night, and can be related to muscle fatigue, dehydration, or electrolyte imbalances. The age of the patient and the nature of the complaint make this a highly probable diagnosis.

Electrolyte imbalance (e.g., hypokalemia, hypomagnesemia, hyponatremia): These imbalances can cause muscle cramps and are relatively common in elderly patients due to various factors, including medication side effects, dietary deficiencies, and underlying medical conditions.
Medication side effects: Certain medications, such as diuretics, beta-agonists, and statins, can cause leg cramps as a side effect. Given the likelihood of polypharmacy in a 74-year-old, this is a plausible explanation.
Peripheral artery disease (PAD): While more commonly associated with intermittent claudication, severe PAD could potentially cause cramp-like symptoms in the legs, especially during exertion.

Deep vein thrombosis (DVT): Although DVT typically presents with swelling, redness, and warmth of the affected limb, it can sometimes cause cramp-like pain. Missing a DVT could lead to potentially fatal pulmonary embolism.
Compartment syndrome: This is a medical emergency that could present with severe pain and cramping, among other symptoms. Early diagnosis is crucial to prevent long-term damage.
Neurological conditions (e.g., peripheral neuropathy, radiculopathy): Certain neurological conditions can cause cramp-like symptoms. While less common, these conditions can significantly impact quality of life and may require specific treatments.

Sarcoidosis: This autoimmune disease can cause a wide range of symptoms, including muscle cramps, though it is less common.
Hypothyroidism: Severe, untreated hypothyroidism can lead to muscle cramps among many other symptoms.
Amyloidosis: A group of diseases that can cause muscle cramps, among other systemic symptoms, though it is relatively rare.