Hi Essential hypertension is the most common cause of hypertension in elderly. A hypertension which is difficult to control with multiple drugs ( is called resistant hypertension) is suggestive of secondary hypertension ( due to some primary diseases like kidney disease etc.) Since your mom is taking clonidine she may be a case of secondary hypertension because clonidine is a regular antihypertensive drug prescribed to kidney patients ( but this assumption is not absolute). Phaeochromocytoma is not a common disease and it presents with episodes of high bp with normal bp in between, Episodic attack consisting of pallor or flushing, palpitations, sweating, head ache and anxiety, Abdominal pain and vomiting Constipation Weight loss Abnormal blood sugar etc. So you can talk with the treating doctor and you can ask regarding the underlying primary disease. If you are still suspecting phaeochromocytoma because of some features listed above, you can share this idea with treating doctor and he will order the relevant investigations if required. Thank you