Her only complaint is a rash on her buttocks.
 The patient has allergic dermatitis.
(ROOT (S (NP (PRP$ Her) (JJ only) (NN complaint)) (VP (VBZ is) (NP (NP (DT a) (NN rash)) (PP (IN on) (NP (PRP$ her) (NNS buttocks))))) (. .)))
(ROOT (S (NP (DT The) (NN patient)) (VP (VBZ has) (NP (JJ allergic) (NN dermatitis))) (. .)))
( ( Her ( only complaint ) ) ( ( is ( ( a rash ) ( on ( her buttocks ) ) ) ) . ) )
( ( The patient ) ( ( has ( allergic dermatitis ) ) . ) )