Causes of Erythema Nodosum (Medical Mnemonics)

Fig 1: Erythema Nodosum

NODOOSSSUM

N	NSAIDs
O	Oral contraceptive pills
D	Darling's disease (Histoplasmosis)
O	Ohio valley disase
O	COccidiodomycosis
S	Sulphonamides
S	Strep A Haemolytic
S	Syphilis
S	Sarcoidosis
U	Ulcerative COlitis
M	Mycobacterium TB
M	RheuMatic Fever

Also Pregnancy

Further Reading | Fig 1

Lichen Planus

Fig 1: Lichen Planus

Lichen planus is characterised by an itchy, purplish, polygonal, flat-topped rash developing over the wrists and ankles. A lacy fine network of papules develops in over 60% of the patients.

It is commonly seen in patients with autoimmune chronic liver disease such as primary biliary cirrhosis and chronic active hepatitis. 

Fig 2: Wickham's Striae

The presence of  Wickham’s striae – a fine, white lacy pattern, over the papules helps in diagnosis. It usually resolves in 12–18 months.